So I went to accurately redo all the rosters, but I'm not sure how to get the right players onto the right teams without trading.(i.e. how do I get Deion Branch onto the Seahawks).
Also, when I'm in the offseason how do I actually do the draft and not just have the computer simulate through it.

Here is how you update the rosters (providing you have access to Xbox Live)...

Go to the online mode, and create a game or senario, you will be asked to download the latest rosters, or you cannot continue. Save the download, and load your rosters from that file whenever you start. Rosters updated weekly I believe.