Need Xbox 360 flashing help

Ok so I have a flashed 360 that I bought a while back but i am running iextreme 1.61 I think because the guy I bought it from had it flashed but didnt know the firmware. I patch the games to wave 3 so that's why I think it's 1.61. I need to update to the newest firmware (iextreme LT plus) to play the newer games but I haven't ever flashed a xbox before. So I guess I need a good tut on how to do it and the tools. I have a lite-on drive. I have a prep $25 visa card for all the supplies and a good tut. Thanks- Funk