Storage issue in ubuntu installation

Question

I have a dell inspiron 5423 laptop with 500GB of hard disk and 6gb of memory.

I had ubuntu 15.10. It was running very slow. I then decided to reinstall ubuntu 16.04. My ubuntu is working fast but always show me "your storage space is running out, you have 900 mb left".

I took the screenshot if i had my ubuntu installed properly or not. If there is problem how can i fix this. I see linux multiple times when doing fdisk -l. When i do df / -h, i get the following

/dev/sdb1 24G 18G 4.6G 80% /

I have attached the screenshot below with disk configuration(sorry for long information)

*-disk
             description: ATA Disk
             product: Hitachi HTS54505
             vendor: Hitachi
             physical id: 0.0.0
             bus info: scsi@0:0.0.0
             logical name: /dev/sda
             version: A7A0
             size: 465GiB (500GB)
             capabilities: partitioned partitioned:dos
             configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096 signature=bea99cd7
           *-volume:0
                description: EXT4 volume
                vendor: Linux
                physical id: 1
                bus info: scsi@0:0.0.0,1
                logical name: /dev/sda1
                version: 1.0
                serial: 587b0ba7-5820-4ae1-9e31-6a0d8667504e
                size: 93GiB
                capacity: 93GiB
                capabilities: primary bootable journaled extended_attributes large_files huge_files dir_nlink recover extents ext4 ext2 initialized
                configuration: created=2015-01-01 21:46:52 filesystem=ext4 lastmountpoint=/media/tushant/587b0ba7-5820-4ae1-9e31-6a0d8667504e modified=2017-02-17 12:40:39 mounted=2017-02-17 12:40:39 state=clean
           *-volume:1
                description: Extended partition
                physical id: 2
                bus info: scsi@0:0.0.0,2
                logical name: /dev/sda2
                size: 372GiB
                capacity: 372GiB
                capabilities: primary extended partitioned partitioned:extended
              *-logicalvolume:0
                   description: Linux swap / Solaris partition
                   physical id: 5
                   logical name: /dev/sda5
                   capacity: 977MiB
                   capabilities: nofs
              *-logicalvolume:1
                   description: Linux filesystem partition
                   physical id: 6
                   logical name: /dev/sda6
                   capacity: 93GiB
              *-logicalvolume:2
                   description: HPFS/NTFS partition
                   physical id: 7
                   logical name: /dev/sda7
                   capacity: 146GiB
              *-logicalvolume:3
                   description: HPFS/NTFS partition
                   physical id: 8
                   logical name: /dev/sda8
                   logical name: /media/tushant/Important
                   capacity: 132GiB
                   configuration: mount.fstype=fuseblk mount.options=rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096 state=mounted
     *-scsi:1
          physical id: 2
          logical name: scsi1
          capabilities: emulated
        *-disk
             description: ATA Disk
             product: SAMSUNG SSD PM83
             physical id: 0.0.0
             bus info: scsi@1:0.0.0
             logical name: /dev/sdb
             version: 2D1Q
             serial: S0XLNSAC532389
             size: 29GiB (32GB)
             capabilities: partitioned partitioned:dos
             configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512 signature=a6921274
           *-volume:0
                description: EXT4 volume
                vendor: Linux
                physical id: 1
                bus info: scsi@1:0.0.0,1
                logical name: /dev/sdb1
                logical name: /
                version: 1.0
                serial: 04f20ec1-3497-43e8-ac80-2616b302dabd
                size: 24GiB
                capacity: 24GiB
                capabilities: primary bootable journaled extended_attributes large_files huge_files dir_nlink recover extents ext4 ext2 initialized
                configuration: created=2016-08-31 17:22:39 filesystem=ext4 lastmountpoint=/ modified=2017-05-29 07:45:19 mount.fstype=ext4 mount.options=rw,relatime,errors=remount-ro,data=ordered mounted=2017-05-29 07:45:20 state=mounted
           *-volume:1
                description: Extended partition
                physical id: 2
                bus info: scsi@1:0.0.0,2
                logical name: /dev/sdb2
                size: 5736MiB
                capacity: 5736MiB
                capabilities: primary extended partitioned partitioned:extended
              *-logicalvolume
                   description: Linux swap / Solaris partition
                   physical id: 5
                   logical name: /dev/sdb5
                   capacity: 5736MiB
                   capabilities: nofs

UPDATED

Model: ATA Hitachi HTS54505 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags: 

Number  Start   End    Size    Type      File system     Flags
 1      1049kB  100GB  100GB   primary   ext4            boot
 2      100GB   500GB  400GB   extended
 5      100GB   101GB  1024MB  logical   linux-swap(v1)
 6      101GB   201GB  100GB   logical   ext4
 7      201GB   358GB  157GB   logical   ntfs
 8      358GB   500GB  142GB   logical   ntfs


Model: ATA SAMSUNG SSD PM83 (scsi)
Disk /dev/sdb: 32.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type      File system     Flags
 1      1049kB  26.0GB  26.0GB  primary   ext4            boot
 2      26.0GB  32.0GB  6015MB  extended
 5      26.0GB  32.0GB  6015MB  logical   linux-swap(v1)