When I try to change my avatar picture, it keeps saying it can't be more than 30kb or something. I cleared cache yet it keeps happening. Someone help?

It means your avatar can't excess 30 kilobytes (kb) in size. What's the image you want to change it to?

It's a picture I took with FastStone Capture, and it's been put in a file I have.

If you upload it I'll resize it to avatar size.

I know it's maybe out of topic, but why my avatar shows as a black box? Can any1 see it? :/

It's because the forums sometimes show an older avatar, and if you did not have one it shows a black box.