Ok first,you should have active sync installed on PC (xp & under) or WMDC(vista & up).Then I suggest you read through the first few post just to understand the terms and what not
http://forum.ppcgeeks.com/showthread.php?t=42503
Now dl this EXE. file to your PC (this is the unlocker)
http://forum.ppcgeeks.com/attachment...2&d=1225515125
now the unlocking process will just be have your phone and establish active sync connection with device and pc.then you will run the .EXE file ,it pretty much walks you through it.give it a few minutes for it to start from 0%.
By now you should have already been through the CDMA Upgrade threads and found a few that you like,find one from this page
http://forum.ppcgeeks.com/forumdisplay.php?f=68 and DL it i suggest mighty rom just to be simple and pretty stock.
now Your phone should be unlocked and you should have a ROM Dled already.Now you will run the .EXE file of the ROM like you did with the unlocker and you will have your first flash.
Keep in mind its pretty hard to brick your device but the easiest way to do so is using ROMS or UNlockers not intended for your device.your phone is sprint so always make sure roms and unlockers are for CDMA NOT gsm.good luck.