Hi Dylbot, I haven't been here very long and am sure there is a thread or info somewhere describing it but the way most people do it is by drilling out the rivets in the base (usually 2) then the base should pop off the carbody. If the base is plastic you will be able to cut the tabs that hold the axle in place, but if the base is metal you may need to use a dremel or similar tool. Then just swap out the axle/wheels with another set from a different car etc.
Hope I've explained my self correctly. Hope this helped you.
Start by drillin out the rivits,then remove the tabs that hold the axel in place. I have found that a dremal tool works the best. I also use JB Weld puddy to replace the rivits when I put it back together. Others may give you more and/or better details or ways to do this. Good luck.