Does a dealer have to change the transmission fluid in a Chevy cavalier or can you do it yourself?

If you want to do it yourself, go to this site. It has step by step information on how to change your Transmission Fluid if you have an automatic transmission without a dipstick.

http://www.j-body.org/forums/read.php?f=11&i=88582&t=88570#88582

If you are not comfortable with changing your fluid yourself, go to a dealership