Ok, finished. Here is how it went down. Firstly, I made the two layers, with Bob Ross as the background. Then I resized the painting til it looked about the right size.
Then I moved the painting over to the one in the background, and skewed it so it fit the back one and covered the old one up completely.
That's when it started to get tricky. I decided to make the painting layer semi-transparent, so I could see Bob Ross behind it. Then I started lasso around Bob and deleting anything from the new painting that covered him. It was hard, and took a lot of undo-ing before I thought it looked right. There were some spots that I erased that I shouldn't have, so I had to paint over them with colors that matched the background.
And that was it. Here is the finished project. Thank you for reading.