Let's do a step-by-step here.
1. Do you have the cue in hand?
2. If so, remove the bumper.
3. Is there a weight bolt?
4. If so, can you unscrew it with a screwdriver?
5. If so, screw it out.
6. Purchase a heavier, or lighter weight bolt, and reverse this process.
Note: If you cannot do the above, see your friendly neighborhood cue repair person.