My Riding Lawn Mower Cuts The Grass Unevenly. How Do I Adjust It?

I have a Craftsman TS1000 riding lawn mower and my son ran over a large rock that damaged one of the two blades. After replacing the damaged blade, the lawn mower cuts unevenly. I put the lawn mower on a level surface and can see that the mower deck is uneven, but I don’t know how to adjust it. Can you help me?