Do your research, prepare to show your report to the manager.
Before negotiating with the manager, make your bottom line first. For example, if you know the current rent is $799, assume you are going to move out, then you have to pay $400 something to cover the moving cost and other tedious settling down tasks. So you may decide to stay here and give out the $400 to the landlord for saving your settle down works. That means you should be willing to pay around $830 for your new contract.
The manager will accept your reasonable offer, I believe.
Please share us your final result later.