I'm on Ubuntu 15.10. My current partition state is as shown in the image.
I had Ubuntu 12.04 installed on a 19.22 GB partition, and I removed it and deleted the partition. Now I want to extend /dev/sda2 to include the 19.22 GB unallocated space that's right after it. However, GParted won't let me do that.
I think it has something to do with the hierarchical way the partitions are presented (the unallocated space seems to be a part of /dev/sda4 somehow), but I have no idea how to solve this.