If your network service provider does not charge you a fixed fee for data transfer, there are a few things you can do to reduce your data usage (also presented on this video (English) from Nokia Care).
Change mail sync settings: If your phone syncs mail frequently, it uses more data. You can choose how often your phone automatically syncs mail.
- Tap the mail account whose settings you want to change.
- Tap the 3 dots (...) at the bottom right of the screen.
- Select Settings > Sync settings.
- Tap Download new content, and select a time. If you don't want your phone to sync mail automatically, select Manually.
If you have installed apps, such as news or weather apps, they may use data by syncing content. Make sure to check the sync settings and feedback sending options of the apps you have installed. Go to Settings, swipe left to Applications tab, and check the settings of the apps.
Check data roaming settings: Connecting to the internet when roaming, especially when abroad, can raise data costs substantially. Data roaming means using your phone to receive data over networks that your network service provider does not own or operate. To make sure you are not using your phone to roam, on the start screen, swipe left, tap Settings > Mobile network (cellular), and switch Data roaming options to Don’t roam.
Switch your mobile data connection off: If you want to make sure you’re not using data at all, you can switch your data connection off altogether. Tap Settings > Mobile network (cellular), and switch Data connection to Off.