Here is a step-by-step guide on how to paint a bathtub:

1. Clean the tub with lime or powdered cleanser and sand it a little.
2. Cover the fixtures, shower heads, tiles, and walls with painter's tape and paper or plastic.
3. Mix the paint with hardener and thinner according to the instructions.
4. Use a spray gun, a paintbrush, or a small roller to apply the paint in two coats, starting from the top corner and working your way across and down.
5. Alternate horizontal and vertical strokes and use a sponge brush for the edges.
6. Finish with a commercial epoxy thinner for more durability.

Here is an article that goes into more detail on how to paint your bathtub step-by-step . I hope this helps!