For those without the update, just set your clocks manually, and set the date ONE month ahead this one time. Second, turn on and CONNECT to wifi. Yes, it only works, to download, on wifi. Third, press on: "Att software update". Last thing, always make sure your phone is backed up, as is better safe than sorry. Once your done, set your time and dates normally.
Note: It's always best to advance your date no more than you need. Not a big thing, but it's best to be ready once the new update comes. Maybe new KitKat, but at least Sense 6.0. Remember, HTC will unveil the second generation HTC One on March 25th. Sale probably in April. As I write this, it's March 1st, 2014.
Good luck!