From the Settings app, tap Connections.
Tap Data usage.
Tap Data warning & limit.
From this screen, you can limit your data usage and set up alerts for when you're reaching your data usage limits for the current month.
Tap or slide the Alert me switch to ON.
You can also turn off mobile data when you're in areas where you don't want to use any data.
Tap OK.
Tap Data warning.
Enter your preferred data usage warning and tap SET.
Tap or slide the Set data limit switch to ON.
Tap OK.
Tap Data limit.
Enter your preferred data usage limit and tap SET.
Tap Cellular data usage cycle.
Select a new usage cycle reset date and tap SET.
We recommend you match this date to the date your carrier's Billing Cycle starts to more accurately manage your data.
You've completed the steps!
