The update will be available either via an OTA update or by syncing to your PC and using Kies. Don't underestimate the ease of an OTA update. There could be one typo involved with the update. Both the OS on the unit in the box and the update are listed as Android 4.0.3 which wouldn't matter except that current production models are using Android 4.0.4.
To get the update, either via OTA or Kies, you need to have you battery filled at 50% or higher, so keep your plug in for the first few days after you get your device.
source: T-Mobile via AndroidCentral