Replacing Pre-amp of 1995 SR500 Ibanez Bass

It's my first time and I needsome help please. I need to replace my pre-amp.
1. Do I only replace the Pre-amp.
2. Do I replace the pick-ups as well?
3. The replacement must fit my existing pot holes of the guitar (4 Knobs)
4. Any suggestions if I want:
4.1 a more jassy sound