The flanged bearing on the gear should slide off. If it's a good fit, use a small flat tip between the bearing and gear to get it working.
The gear and shaft should have come as an assembly, with a separate gear for the input side.
You'll see a setscrew in the end of the shaft, which holds the cross pin in place. Removal of these will allow the removal of the gear from the shaft.
The gear and shaft come as an assembly, because we turn the OD of the gear to fit the bearing while installed on the shaft. We found that by just replacing the gear may cause an out of round condition, which leads to vibrations. Especially spinning at about 8,000 RPM.
Chris D. Bergen