Disk management shows 4 NTFS partitions (C: D: E: and F:), these 4 are windows partitions that you have created, and there are 2 other partitions for which the file system is not listed here, these belong to your Linux system, the one with 12.01 GB is where your root directory (/) is mounted, in other words that is your Ubuntu OS, the other partition is your SWAP partition, this is used by the system in a way similar to virtual memory in Windows.
If you want to uninstall Ubuntu, there are different ways to do this, the way i'll do this task is as follows:
You'll have to use Windows to delete the Ubuntu Partitions.. seems an easy task but be careful, when you installed Ubuntu, the boot manager (GRUB for Ubuntu) was also installed and is the purple screen you see at boot time with the OS Options to select from, so if you remove your Ubuntu partitions this will also go away and your computer will not boot... don't panic!
You'll then have to use your Windows installation disk to repair the MBR (Master Boot Record) so that Windows can boot again.
Uninstalling Ubuntu may not be the best solution, there are many great websites that provide excellent help on how to resolve issues that you may find in your way. We are a great community eager to help and to share the things we have learned.
You can find more information about dual booting and boot managers here:
It's a graphical explanation about partitions, boot managers and installation of different OS's that may help as well.
Hope this helps.