How to convert Canon Vixia video files for editing?

My Canon Vixia HF R100 came with software called Pixela ImageMixer and when I try to edit my videos in it, it's extremely slow! I don't know if that's because the files are huge and my computer is slow, but I'm more comfortable with other video editing software, like WMM or Vegas Movie Studio. How do I convert my HD footage to SD so that my computer doesn't get slow or die, and how do I convert the files to wmv or something so I can import it into most video editing programs? I plan to upload it to youtube when it's done.