I tried clicking 'software update'

http://1drv.ms/1fJ5B3h (short video showing steps I've done)

http://www.htc.com/us/support/htc-one-x-att/news/

Navigate to the Home screen then tap All apps > Settings > About > Software Information and locate the Software version. If your Software number is less than 5.18.502.1, you should proceed with the upgrade.

I tried updating via 'HTC sync'

This phone belongs to my employer and I was advised agains breaking the warranty. So the recommended / official way of updating software is preferred.

I tried inserting another (not AT&T) SIM and it tells me that it is locked. Is that a case that software update doesn't work without the SIM?

Thank you

I tried clicking 'software update'

http://1drv.ms/1fJ5B3h (short video showing steps I've done)

http://www.htc.com/us/support/htc-one-x-att/news/

Navigate to the Home screen then tap All apps > Settings > About > Software Information and locate the Software version. If your Software number is less than 5.18.502.1, you should proceed with the upgrade.

I tried updating via 'HTC sync'

This phone belongs to my employer and I was advised agains breaking the warranty. So the recommended / official way of updating software is preferred.

I tried inserting another (not AT&T) SIM and it tells me that it is locked. Is that a case that software update doesn't work without the SIM?