Howard, sorry for the long delay in replying.
There are a coupe of ways of dealing with this.
The first and probably easiest to start with is to remove the black plastic end caps from each hinge, carefully with a small flat bladed screwdriver.
Get a kettle of boiling water and pour over the top hinge, at the same time moving the door backwards and forwards (be careful not to spill the hot water over yourself), follow the hot water with WD40, again rocking the door backwards and forwards.
Do this with each hinge until they move smoothly, then give each hinge a good dose of 3in1 oil.
You may have to repeat the hot water application several times, along with more WD40 to get all the rust out.
The long way is to drill out the rivets holding the hinge and strip the hinges on a work bench, remove th erust from th epivot pin, grease and replace with new rivets.