There's no way to do a scene swap just on the M13 itself. You can do it through MIDI, though. You'd just have to back up one of the scene via MIDI first, copy the first one to the second location. Than go back to the first one and load the second one to that location. When you load a single scene onto the M13, it saves over whatever scene is currently active.

The instructions how to do this can be found here: http://line6.com/support/docs/DOC-1806