The 344MB update has started rolling out on Thursday, albeit in stages. This means that some patience is required if it has not yet hit your phablet. You can look for the update by going to Settings > About Phone > Software update > Check now. Before downloading and installing the update, make sure your battery is at least 75% charged. And you might want to be on a Wi-Fi connection during the entire process. This way, you won't be using up any of your precious monthly data allowance by updating your HTC One max.
Sprint starts rolling out Android 4.4.2 to the HTC One max
source: Sprint via MobileBurn, Engadget