HTC One M8 for Windows - Manual (Page 163)

Connectivity
Data connection
When you turn on your phone for the first time, it will be automatically set
up to use the Verizon Wireless mobile network.
Turning the data connection on or off
Turning your data connection off can help save battery life. However, if you
don’t have data connection turned on and you’re also not connected to a
Wi-Fi network, you won’t receive automatic updates to your email, social
network accounts, and other synchronized information.
1. Swipe down from the top edge of the screen with one finger.
2. Tap All settings > cellular+SIM.
3. Tap the Data connection On/Off switch.
Connectivity 163