There is a c shaped clip with tabs that hold the crank handle to the shaft. There is a window crank removal tool that slides in just under the handle while lined up with the window crank, if the clip was put on properly. If not you insert the tool from the opposite side. Once the clip is pushed off the handle remove the tool and pull the handle off.
If you do not have a tool a small hook will do. Put a screwdriver or putty knife between the handle and the door panel from the side of the handle and create a small gap so you can look down and see the clip. Hook it and give a tug and pull the clip out. The handle will come off.
To reinstall the clip just push it back in place on the handle, line up the handle where you want it to be, and just push/snap it back on.
Be carefull not to mar the door panel, And don't loose the clip. You can get more clips in most parts stores.