How to switch E0 to E1 for extruder?
If you go through the Repetier-Firmware configuration tool for version 1.0.2 you can select the E1 stepper for the E0 extruder (or whatever stepper you want to use for it) in the tools tab sheet. I'm not familiar with Repetier, but if that does not work you would have to switch pin numbers. 

If you already have a Configuration.h, you can use that one (by loading it into the configuration tool) and alter the E1 afterwards so that you do not have to enter all the other options by yourself.

Edit: After some investigation, you can find your configuration file here as described here, so the only thing you would have to do is to load the file in the online tool and adjust the E1 stepper for E0 extruder.