Default HTC one v flash from virgin mobil to verizon or straight talk


I just go this phone and the guy said it would be simple to flash it to a new carrier. I have been all over this forum and I don't even know what to look for or how. He told me to do something with the rom and to get TWRP or something. I honestly don't know where to begin. I can use computers but I don't know much about these phones. I also checked on cyanogen but it seems this phone may not be supported. Can someone help? I just read some posts and saw it would help to know that it is GSM.