Use a heat gun or hair dryer to heat the rubber roller until it's hot to the touch.

Prop the roller bar up against a sturdy surface or have someone hold it.

Place the open end of a wrench around the roller bar, above the rubber roller, so it rests on the roller. The wrench needs to be big enough to fit around the roller bar while still resting on the rubber roller.

While holding the wrench with one hand, use a rubber mallet to hit the wrench and push on the rubber roller until it slides off of the bar.