How can I paint or redo my fiberglass units in my bathroom?

I just replaced my 1981 fiberglass/shower with a new one. We had to cut apart the old unit with a reciprocating saw to get it out because it was one piece and installed before any doors were in place. We purchased a new tub/shower combo that came in 4 pieces for remodel installation. This combo unit was approximately 550.00. We were able to set the tub and shower walls ourselves and then have a plumber come and finish up the plumbing--with just a few changes. There was some sheet rock repair to do when we were finished with the tub and plumbing. If you are a good DIYer you can do much of this yourself.

https://www.homedepot.com/p/Delta-Classic-400-32-in-x-60-in-x-80-in-Standard-Fit-Bath-and-Shower-Kit-with-Left-Hand-Drain-in-White-BVS400L/301423675

Really need to replace, they are not meant to last more than 15 to 20 years. You've gotten a good life out of it. Don't expect the news one to last that long.