From within the Settings app, tap Mobile network.
Tap Data usage.
You can also turn off mobile data when you're in areas where you don't want to use any data.
Tap Data usage limit.
Tap Daily data usage 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 the daily data usage limit field.
Enter your preferred daily data usage limit.
Tap the Check icon.
Tap Monthly data usage limit.
Tap the monthly data usage limit field.
Enter your preferred monthly data usage limit.
Tap the Check icon.
Tap Start calculating data usage from.
Select your preferred data usage cycle reset date.
We recommend you match this date to the date your billing cycle starts to more accurately manage your data.
Tap OK.
You've completed the steps!
