If your Sony Xperia Z Ultra C6802 is not good for work, please try the following ways to reset your Sony Xperia Z Ultra C6802:
You need to charge your battery, remember to backup your Sony Xperia Z Ultra C6802’s important data and in most cases take out SIM and SD card. It is always very important to backup online, because it is impossible to recover your data after doing a hard reset. For all of your data, a backup should be done on an external device, hard drive, raid system or media. Ensure that your important data is backed up in a safe place.
press the Menu key
-scroll to and choose Privacy
-scroll to and choose Factory Data Reset
-choose Reset Phone
-choose Erase Everything
And always remember that this will reset everything back to factory default settings, remember to backup your Sony Xperia Z Ultra C6802’s important data at first.