Only way is to remove paint by ruining can. Here is the method I use which I think is pretty safe. To be sure all propellent is gone, I hold down nozzle to prevent buildup of pressure while I take a sharp punch and punch a big hole in can. I then clean up the hole with a reamer to smooth edges of hole. I let it sit for awhile to make sure any residual propellent boils out of paint and then pour out paint through hole.