Right now you can only use custom/cooked 6.5 rom, as official one not out yet.
First, go to the
CDMA TP2 Upgrades section and read thread title "CDMA Worldphone HardSPL Unlocker" to find out how to unlock your phone so it can flash custom roms.
Then download one of the custom rom posted in the same section. You can flash from your computer, but there is another sticky thread about how to flash rom from your phone without computer.