posting affiliate banners

When I first started my page my banners were appearng. Posting the inital 2 banners went just fine. Tyring to post additional banners is where the problem started. I didnt quite understand how to post and where to post the different banner sizes. I got all confused and now nothing is posting. I think I may have deleted the inital code that was in the affiliate banner code 1,2 and 3. Somebody help! How do I get them to appear again?