At&t failing 5.1 update

Just bought an at&t variant on craigslist, I did a factory reset and tried to run the 5.1 update and I get an error updating, it downloads update.. then it reboots and starts installing showing the android guy working , then about 20 seconds into it it shows the little android guy on his back with a red exclamation and says error and then proceeds to reboot. Once rebooted it says it failed to update. I'm used to Samsung phones .. hoping there's an odin type option to get a stock 5.1 or rooted stock 5.1 on this guy, any headstart info would be appreciated. thanks