I don't know their model numbers so I don't know what type control valve is on your softener but... if it unclamps or unscrews from the tank, you should be able to replace the resin fairy easily. If the control has two collars covering dovetail type tank connectors, then it is fairy difficult for a DIYer to replace the resin. But it may not be the resin.
Does it use salt? If not poke a stick down through the salt to see if there is a hollow spot under the salt keeping the salt up out of the water. That would be a salt bridge. Other causes of not usign salt are a blocked drain line or injector, injector throat or injector screen. Is there more water in the brine tank than is normally in it?
Post a picture of the tank to control valve area and the face without the cover on it.
If you get around to a new softener, I suggest one using the Clack WS-1 or Fleck 7000SE control valve. IMO they are the best choice for any DIYer.
Quality Water Associates