How to update an unlocked at&t htc one m8?

[Dolvera]

I have an at&t unlocked htc one m8
android version 4.4.2
HTC sense 6.0
Software number 1.12.502.18

I live in Mexico so OTA updates from AT&T don't work, everytime I try searching for new updates from the device it says that there isn't any and that the device will search again in 24 hours.
I dont know if this is relevant but I rooted my m8 because I wanted to change it to google play edition but i couldn't get s-off because firewater method doesn't work anymore.

Ive tried AT&T RUU from htc site but i got error 155 and i didn't want to continue because I don't want to screw my m8.
Im a newbie and I would really appreciate some advice :c

 

[itguyjax8430]

I have an at&t unlocked htc one m8
android version 4.4.2
HTC sense 6.0
Software number 1.12.502.18

I live in Mexico so OTA updates from AT&T don't work, everytime I try searching for new updates from the device it says that there isn't any and that the device will search again in 24 hours.
I dont know if this is relevant but I rooted my m8 because I wanted to change it to google play edition but i couldn't get s-off because firewater method doesn't work anymore.

Ive tried AT&T RUU from htc site but i got error 155 and i didn't want to continue because I don't want to screw my m8.
Im a newbie and I would really appreciate some advice :c

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Do you have a custom recovery installed on your phone?