Bathtubs are heavy items and removing them from their existing homes can be a challenging task. However, with a little know-how, you can safely and efficiently remove an old tub and install your new one without any additional cost or damage.
Before attempting to remove the old bathtub, make sure that it is fully disconnected from all of its water and drain lines. After that, have a helper take the tub by its flange and gently begin to pull it away from the wall. You may need to wiggle it back and forth as you pull it. Once it’s loose enough, use a pry bar to remove the remaining screws and nails fastening it to the wall. 
When you’ve got the tub completely free, use a level to ensure that it is perfectly horizontal. Once it is, mark the wall where the top of the new bathtub will fall (or the rim). Make note of that location so you can easily attach the tub surround to it once it’s set down.
While you have the tub removed, clean the floor around it to make sure it’s free of mold and other debris that could be trapped underneath the tub. Also, at this point, you should patch the floor as needed to prepare it for the new tub.
If your old tub was not installed properly, the back wall where the flange is located should be framed to support the new tub. Make a mark on this wall at the top of the ledge where the new tub will rest, and then cut a 2×4 down to size to fit on the back wall (Photo 1). This will be called a stringer board and it will be used to support the new tub (Photo 2). For more information about tub installation, Bathtub Installation Sacramento can help you process with everything you need.
You will now need to screw this piece of framing into the studs that are holding the ledge where your new tub will be sitting. Use 2” coated exterior construction screws to do this. Before you attach this, check your tub manufacturer’s instructions for any nuances that may apply to the installation of their particular model (Photo 2).
Once the stringer is in place, go ahead and screw the new tub surround to it. Before you do, run a bead of clear or colored silicone caulk on the ledge of the tub where it meets the tile and push it into the gap. This will create a rubber seal and help to prevent the tub from moving on its own over time.
Once the caulk is dry, have a helper lift your tub by its flange and lower it to the floor. At this point, it’s a good idea to have your helper try running a full-water test to make sure that the new drain seals properly. If it doesn’t, you’ll need to re-caulk that area and double-check the drain.