Can anyone help me get Repetier up and running on my Pegasus?

I've been using Repetier on some of my other printers. I need to calibrate my steps/mm on my extruder and I think the easiest way to do this is to get Repetier up and running and adjust the firmware from there. I'm not quite sure how to start though. I've tried connecting with Repetier and it just crashes. I assume I might need to adjust something in the firmware first then try to connect but I am at a loss.

Update: I have Repetier Host running and interacting with the printer. My problem seemed to be with Windows 10 so I had to run compatibility mode and run it in Windows 8 (7 probably works fine too). There was no need to update the firmware or download additional drivers. Everything seems to be working fine and I will update again once I get some settings dialed in.

Alright, I've got it working pretty good now. If you have your settings from the stock slic3r ini files for the Pegasus all you have to do is go into Repetier and connect to your printer (granted you've figured out how to do this, if you need help post below), head over to the slicer tab and click on manager. This will bring up a submenu that asks for the Slic3r Config Directory, hit browse and head to wherever you unzipped your original slic3r configs. You should be all set after that. I opted to duplicate the configs and change their names but you can do whatever you like.