How do i take out a shower stall and install a tub and shower unit??

If it's one of the fiberglass inserts, you'll need to score about an inch out all around the frame. There is a plastic piece that is under your dry wall attached to the studs. Once it's out you should be good to go.

You need at least 5' to install the tub. That is the opposite of what I did. I took out a tub/shower and made a big shower. You may need to move plumbing drains. You will probably need to open the wall for the water supplies. The floor needs to be able to support the weight of the tub with water. New wall treatment will be needed.