1. Go to "System Settings"
2. Click on "Data Usage"
3. Turn on "Mobile Data" (assuming that its off)
4. Click on the present date mentioned in "Data usage cycle"
5. If you cannot see the option "change cycle" after following the step 4 then click back button to exit the screen and then click on "Data Usage" again and then click on the present date mentioned in "Data usage cycle"
6. You should now see "Change Cycle" option.
Note : On data usage cycle enter todays date to reset the data usage