Ok, so firstly I'm using Windows 10/Ubuntu 16.04 LTS. Before anyone asks, the unallocated space is not by the Ubuntu partition, it is by the Windows partition, which makes this more difficult. I had looked at doing this while in Windows, but Windows disk manager doesn't show EXT4, and EXT2 volume manager doesn't show unallocated space so...
Here's a screenshot of Windows disk manager (the 27.60 GB is Ubuntu)
And here's EXT2 volume manager
I'll try and get a screenshot of GParted within 30 minutes, if that helps. Thanks.
Edit: Here's the GParted screenshot.
Possibly relevant, but the Windows partition lists the error "Unable to read the contents of this file system!" Any idea about that?
Edit 2: Another update! Partial success so far, after shrinking the Windows partition I gained about 40GB, which I merged with the Ubuntu partition. There's still 12GB by the Windows, but unfortunately I keep getting an error whole trying to move Windows. I'll figure that out soon. :) Thanks!