I think that this is one of the easiest mods to do to your car. It works pretty much the same on zips as it does on bits.
Step 1:
Pretty easy, just disassemble your car, and remove all wheels from the axles.
For the fronts, I just cut the bit wheels off the pins and used two pairs of needlenose pliers to pull the pin out.
Be very careful not to disturb the axle gear, cause you don't want it to wobble around.
Next pull the inner wheels off of the modifier. make sure to keep at least two of the screws
For the rear, I used cigarette rolling papers to make the inner modifier wheels fit on the axle.
Just glue the wheels onto the axles and make sure that they are straight, so the wheels don't wobble.
Wait a couple hours for the glue to cure and put the rear axle back on the car.
For the fronts, it's just a simle matter of using the modifier wheel screws to mount them to the steering knuckles.
Note: you may want to cut the wheel spacer off the steering knuckle to bring the wheels inward, so the body will clear.
I don't recommend lowering the car too much. Other wise you will have to use a dremel to shave the inner fenders so that the wheels will turn properly
Now you're almost finished. Just mount the inner wheels to the steering knuckle using the modifiers wheel screws, and then reassemble everything.
Finally mount the rims to the inner wheels and you're done.
If needed, glue the rims. I don't recommend this unless these are the wheels you want mounted permanently to the car.