Trouble editing categories, deleting categories, etc.

Hi!

So, I had a bunch of categories, including “other” which I renamed from “uncategorized”.

First of all, I cannot remove “other” from individual or bulk posts, and it shows up on all my posts.
Second, when I go to edit a post, it doesn’t show checkmarks next to the categories it’s already applied to, which is why I cannot remove “other.”

I just switched to the Twenty Fourteen theme, (it wasn’t working in my old theme, which was outdated and buggy anyway), and that didn’t fix the problem.

Then I deleted all the categories I had and recreated some. Still fixes nothing.

Ideas?!