Verizon and AT&T unleashed the Android 6.0 Marshmallow update onto their Samsung Galaxy Note5 users in March and towards the end of the same month, Sprint joined in as well. Now it's time for T-Mobile to do its thing - the update is available Over The Air and it weighs in at 1,420MB so make sure to download it over Wi-Fi. Downloading the Marshmallow update for T-Mobile's Galaxy Note5 The update brings the usual Marshmallow goodies and makes the some changes to the pre-installed app package - Facebook Messenger, Instagram and WhatsApp are getting the boot. Source
Source: http://www.gsmarena.com/samsung_galaxy_note_5_for_tmobile_getting_android_60_marshmallow-news-17820.php
