For straight axles I seperate the chassis from the body by drilling the rivets. Then the three tangs (per axle) need to be ground off. I usually use a wore down cutting wheel for this. I usually don't cut the axles as they may fit something else without doing so. If I have to cut the replacement axles I do so after sizing. Then I Krazy Glue them to the chassis. Then I J&B KWIK over that. I'm not that big on rollers but if that's your thing then don't get glue or J&B on the moving parts. Sometimes I also use 1/32 aluminum tube to place the axles but this usually requires modding the chassis to adjust ride height.
If you use a small screwdriver u can pry the tabs up with a twisting motion, then pry up the axel close to the tabs and the axes will pop out. Then pop ur new axels in and use hammer and small punch to squash tabs back down(suport the base so the wheels are not sitting on the surfcace and u get a solid surface to hit) on the new axel. I can do these style swaps 2 to 1 compared to the grind and glue method, both work great but if you can get this down its much FASTER and EASIER.