PHRF lives on information. If you want to change your rating, you need to provide complete information to the board. You also need to refute any suggestion that you are slow because you don't maintain the boat, have a crappy crew, or don't have decent sails. You might also want to explain what happened if you won a race by a big margin in the recent past ("We got a 20 degree wind shift that launched us in the race" kInd of thing.) If you made any big changes, you might benefit from explaining why, if it was not to improve performance. When we made a submission to the board a few years ago, we provided 1. Complete race results for the previous two years, 2. Explanations regarding boat maintenance, 3. Information regarding sail replacements, 4. Brief summaries of crew resumes, and 5. explanations regarding performance extremes.
If you made big changes or if your boat is new to the area, it might be necessary to languish in obscurity for a while in order to accumulate enough data to support a change in your rating.