I recently did this so I could transplant my "good" "turbo" gear from the Zip Zaps rear it was attached to onto my shen so I could keep my wheels matched.

I used a pair of small needle nose pliers to hold the axle once I had pulled off one wheel.
The press-fit from the facotry will be shot now, so have some model glue or super glue handy to re-seat the wheels in the axles.

Make sure you hold the center of the axle, or close to it! If you rough up the axle where chassis holds it, it will perform poorly and wear out the chassis quickly.

I also set up the gear side first and let it dry so I could snap in the axle and adjust the wheel spacing right for minimum sway when I glued in the other wheel. The resulting rear looks great, and has a closer tolerance than when it was new.

I have to repeat here that the Zip Zaps Fast & Furious kit is a great value for the parts you get. I don't even care about the car bodies! The motors, rears and suspensions, not to mention the tires, all have some use for anyone looking to mod!