Some options.
1. Use a bench vise to hold the bearing along, and tap out the gear. I had to do this once with some, from what I can recall. If you do not have a bench wise, improvise
2 bricks and 2 steel rules stategically inserted under the bearing on both sides is one I can imagine.
2. Use a dremel to drill out the old gear. This can also be done manually, if you have the right tools. Since you are going to discard the old gears anyway, this should not be an issue (assuming I understand correctly what you are trying to do).