How do I factory reset my hisense u939 phone

To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.