do you mean step by step to remove or to paint it?
Painting is easy if you're using specialit paints, thoroughly clean the area you're looking at 20 years of grot thats engrained itself, much easier with dash out. Foliatec or other nonstatic type stuff I've found works, not dash cleaner as this is designed to make it look nice and waxes surface. You can also finely sand it to provide a key (don't overdo it though)
Use plastic engraining paint, you need stuff designed to impregnate the plastic so go for something like foliatec or motor factors own brand stuff - test a small out of sight place first, leave it a few days and check if paint has gone on and doesn't bubble, marble, crackle or flake. If alls good paint up with lots of thin dusty coats. Once done you can spray sealer on or leave for a matter finish.