True is, you cannot access ext4 filesystem/partition by windows OS.
my solution is to reduce ubuntu partitions and create ntfs partition which will be shared among all the operating systems. after creating the parititon you can assign drive letter in windows and create a mountpoint in linux (directory which will be pointed to this partition).
use gparted to shrink ext4 partitions or diskmgmt.msc to shrink ntfs partitions (although gparted can handle NTFS partitions, diskmgmt is safer).
(to install it - sudo apt-get install gparted)
DO NOT change or move "System Reserved" partition (a 100MB partition, the first one) because it will ruin your boot process.
also, DO NOT move the partition which holds "/boot" mountpoint (if you chose the default, it's the "/" mountpoint. GRUB might be corrupted after.