Congratulations on purchasing the Nytro. For starters, take a look at the 2nd titled posting on the first page of this FX Nytro General Talk forum. You will find this on page (1). The title is FX Nytro FAQ's. These are called stickies. Open and scroll down to suspension or any other title of interest. There is a lot of good information in there.
I do not own a 2008 but I guess you have rear torsion spring that you can set at (S=soft), (M=Standard), or (H=Hard). Turn this adjuster on both sides of your suspension to a harder setting.
Try to obtain an owners manual. It has good diagrams and talks about the spring preload on your center shock. Increasing the spring preload will harden the suspension.