Use a 5/8 inch box wrench or socket wrench to loosen the nut holding the shaft to the chassis.

A 1/2 inch drive impact driver with 5/8 inch size impact socket may be helpful if the roller nut is rusted at all.

If the shaft is stuck, apply some penetrating oil to help loosen it.

If the shaft spins when you try to loosen the mounting nut, use locking pliers to secure the shaft.