I'll add: To remove the bit of ribbon that is stuck wound around the grey spool, it is not sticky, so you just need to cut it off from the cartridge and use a toothpick to unravel the ribbon.
This was not immediately obvious to me and pulling on the ribbon did nothing for me. (I realize this isn't quite the question being asked here and OP probably already figured this out, but this page was the closest I could find anywhere to finding instructions for removing the stuck ribbon, so others with the same question might also end up here)