Basically you jack up the deck and replace the post. It's hard to tell from the picture but there should be a steel post base to connect the post to the concrete to prevent the post from shifting.

I don't know who built your deck but it looks like it has serious problems with the footings/posts. Though the tenant should have obviously called you and not have tried to fix it themselves. I'd have somebody check the footings and then replace/plumb all the posts.

Thank you both very much! I appreciate the advice! The deck had just been built when we bought the house, but it does look like we will be replacing all of the posts.

My Deck comes off my 2nd floor and was built in 87. Now the deck appears to be settling and I dought they put proper footings in to support the weight of the deck. How costly is it too just have someone raise the deck and replace the post there are about 8 that need to be reset?