Factoty reset deletes all the data, setting, installed app on Android HTC One. It is also known as hard reset, master reset. To do and perform factory reset on HTC One and other HTC devices, follow the instruction
1. Open "Settings" app
2. Find "BackUp & reset" and tap on it
3. Tap on "Reset phone"
4. Make sure to select "Erase All Data" if you want to delete the entire data of your device
5. hit "OK"