open the link

item 40 is part of the adjustment system.
1. Park the mower on your level drive way.
2. Add the correct air pressure to all tires.
3. Position a couple of 2" X 4" boards on each end of the deck.
4. lower the deck on the boards. This will relieve tension on the adjustment mechanism.
5. Find item 40 in the attachment. Remove the pins and rotate the adjustment so that it will lift or lower the affected side.
6. Simple!!!

Of course without looking at your deck, I have no idea if this will work. Mechanical skills are needed to analize the real problem. Something has slipped or perhaps some of the lift linkage is bent. The Murray decks were more complex than some other brands and they were sometimes difficult to keep in adjustment. The turn knobs used to lock the adjustments did not exert enough force and often slipped.

Here is a link that might be useful: deck suspension