Crawl underneath and you'll see a zerk fitting on the bolt that goes through each end of each spring and shackle - should be one on the equalizer between the springs, also. Offhand, I think there are nine on each side. Any good chassis grease will work as this is not a real demanding application. Pump it until fresh grease comes out the back side.
FWIW, several people have reported that their shackle bolts had a dab of red grease on the zerk like it had been greased, but it was actually dry. Mine was that way, too, so I made a point of using black grease to see if any red grease came out - zero, nada, nothing.
If you find a zerk that won't take grease, try taking the weight off that bolt and try again.