Go to My Controls (top page)-> Personal Profile-> To edit the small Image on the left go to your Avatar Settings, to edit the image down your posts go to Edit Signature.
Remember that avatars must be 100x100pixels (max).
And that sigs must be 550x200pixels (max).
To host your images go to http://www.imageshack.us
If you have any more problems with this, post here or send me a PM.