many thanx mike try when bit warmerRollers available from your local caravan accessory shop undo the bolts on the outside end of the roller grip with large pair of grips and wiggle it off the bearing ,good idea to spray the inner end of the roller with penetrating spray leave for a while ,in extreme cases you might have to use an angle grinder to cut the roller off if it is badly corroded on.
Take your old one to the dealer as there are different lengths and don't buy the ones with the red grit.
Hope this helps
Mike.