Download ROM Manager.
Open Rom Manager.
Make Sure You are on most current ClockworkMod Recovery.
Download Rom.
Peter Alfonso
Install the Deodexed "Stock Rooted GWK74".
Wipe Dalvik. Backup Current. (Do Not Wipe Data and Cache- if you were running the Stock Software, you should be fine. That is only usually done when running a custom ROM).
Once it reboots, Open ROM Manager.
Download Rom.
Peter Alfonso.
D720SPRKE1.
Wipe Dalvik. Dont Backup. Dont Wipe Data.
After that you are done.
You may want to install Peter Alfonso's Tethering Fix for Tether.
You will have to reset up your homescreens unless you were running a custom homescreen launcher like Launcher Pro or ADW.
If your phone has a lot of Force Closes then you need to Restore Backup using Rom manager. and make sure you have GRJ90 baseband installed, if not reinstall. Then use Titanium backup to backup all your user apps. Copy Titanium Folder from phone to computer. Do my earlier steps, but when installed GWk74, do wipe data and cache. You will use titanium to get apps back after you install it and bring that folder back over from computer.
Welcome.