How do i take the fiberglass shower out in my bathroom and put in a t?

They are normally installed before the bathroom is completed. That means some tearing out the sheetrock a few inches around it. Also, it probably won't fit through the door to get it outside so you should be prepared to cut it up to remove.

This is quite a project also involving water lines. Is your floor in good shape or does it need repair? Think about your floor! Is it solid? Does it have water damage? Can your floor even hold a full tub of water? Same with walls behind the existing shower. How about the water pipe installation for the tub? When you start this make sure you have budgeted correctly. There are several utube videos to walk you through the process. Watch one and see if this is something you can do. Remember you will need to change how your water drains. Showers are different. This is a project that sounds wonderful when you think about it but it will be challenging. Do your homework and check with a handyman, family member or friend, with regard to the floor, piping, how much your tub will weigh if it’s full of water. Lots to do but do your homework and good luck!!!!!

I think those are installed with construction adhesive. Using a hammer to strike with, poke a hole in the side with a crowbar or a Cat-Claw & pry it & see if it gives up. I'd start with a corner. But if you can't reach one, get as close as possible without stretching. It's going to take leverage & upper-body strength. Cheers!