After the Zenfone 2 Laser, ASUS has also announced the much awaited Android 6.0 Marshmallow update on the ASUS Zenfone Max (ZC550KL). The company did not mention much about the changes you will get on your ASUS Zenfone Max (ZC550KL) but you need to back up all your files and move your photos and videos on MicroSD.
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To update, just go to Settings > About Phone > System Update. Once updated you will no longer have the the ASUS Email, ASUS, Calendar and ASUS Messaging. Instead, you will have Gmail, Google Calendar and Google Messaging. Make sure you have enough power and stable WiFi connection before updating.