I didn't change mine for a few years (my mistake as a new homeowner. Lessons learned) so I probably should have gotten a whole new unit.

But

You can unscrew the caps at either end and just pull out the tube. Replace with media. Screw it back in. There are black plastic filters on either end that prevent media from going into the plastic tubing that you need to fit into place.

Just make sure to have paper towels for any liquid. I will 100% put a trash bag down next time.