Go here to download the Official Sprint Rom:
http://www.htc.com/us/supportdownloa...act=sd&cat=all
OR
Go here and download a custom rom IN EITHER EVENT READ THE DIRECTIONS AND THE POSTS:
http://forum.ppcgeeks.com/forumdisplay.php?f=59
If you arecomfortable with changinging the rom (it's very easy) then use the official rom (if you mess up you are still covered by Sprint) or you can bring your phone into Sprint store and they will do it for you.
There are MANY GREAT Roms here made by some extremely knowledgeable and helpful "CHEFS" and eventually you will, at the least , like many of us less knowledgeable members enjoy upgrading your phone on a regular basis