I changed my banner without huge issues. I only had to make one change after doing it. The font, "PLANET OF THE APELS" doesn't exist. I had to draw it in Illustrator. It was kind of a pain.
Here's my reference:
I changed my button. I was happy that I only had to tweak it in a small way after I uploaded it. I remember the first time I did this I had a headache afterward! All I could get to show up was code and no picture, then picture and no code! You can grab my new button if you like me. ;)
I changed my background color from green to blue. It's my own background, so I did have to go into Photobucket, re-upload and mess with the coding. I was putting it off because I did not remember how I did it in the first place. Once I looked at my html coding; I saw where I had put it.
Ya last year I messed around with my background, and my whole blog disappeared. That didn't happen this time! YAY!
Then I changed my Favicon. I didn't even know what that was a year ago. It's not a bird like it sounds. It's the little planet symbol up above. Nothing fancy, but now you can pick out my blog easier from your other tabs. Here's a great tutorial on making a Favicon.