I just installed an SSD and reinstalled the OS onto it. I wanted to clear my HDD afterwards. However, the Partition on the HDD was still there. I wanted to remove, so I right clicked and deleted, leading to an allocated space. I wanted to extend my HDD to fill up that remaining space, but instead it resulted in two parts and is showing up as Simple Volume.
delete them both and create a new, single, simple volume.
I cant see your pic at work, but if your volume says its a system volume then windows probably wont let you since you are still actually booting from it.