i'm going to edit template. but if i have edited it (changed colors and pictures) i must leave copyright or not?
If you did not own the copyright in the first place you may get in trouble for modifying irrespective of if you leave the copyright logo on there or not.
technically, no you don't. If you change the template enough that it is not identifiable, you are safe. But keep in mind, someone spent time to make the site. Throw them a link and karma will pay you back.
Yes of course leave the copyright. You probably aren't supposed to be editing it anyways if it's a real copyright.
Best to be safe. Its kind of rude to remove copyrights of other peoples coding. Even if you change the colors.