The Quick Explanation
First we unclip the sides, with a screwdriver, or in this case, a bottle opener
Then remove the window in order to take out the sash balance
Remove the sash balance from one side, then the other
Reinstall the window
Re-clip the sides so the sash balances stay in place on each side
This isn't a hard job to do, but it can seem baffling to repair a vinyl window if you've never done it before. Be patient and careful, sometimes it takes more than one pass at this job.