One of the first things to do after a mower purchase is to level and pitch your mower deck. I have never bought a mower where the deck was set up correctly. Look on page 29 of the operators manual. The only bolts that you loosen and adjust are the bolts attaching the deck frame to the deck hanger.
The deck is supposed to float on the hangers. Look at the picture on page 29. You see the slot in the hanger. As the mower goes over uneven ground, the deck wheels will make ground contact and the deck is allowed to rise in those slots. The adjustment is done on the lower bolts, where the hanger mounts to the deck.