For Non-Root Users
If your device is not rooted, then you can not clear the ‘data usage’ without resetting your device to factory settings. But, you can change the data usage cycle and get the desired results. (Well, kind of).
Start by turning on your mobile data first (important), then go to Settings > Data usage > tap on the present date cycle > Change cycle > Select today’s date. This will reset your data from the present date. You can still see the older data usage, though.
Alternative method
To get more control on your data usage, I suggest you try my data manager. It lets you track; which apps is using how much data, how much bandwidth you spend every day/weeks etc.
- TechWiser