Why do you want to do this?
Anyway, the axle is fixed in the shell. To get it apart just twist and pull. As noted above you will need to use some glue to get it back together. A few years back people were doing this to replace the metal axle with a 1/4 inch wooden dowel. Made them play a little nicer. You can remove the caps fairly easily too. There is a small hole at the edge of the cap. You can stick something in there and pry them off.
The only real reason I can think of would be to mod it and add a real axle and bearing.