Hard Reset HTC One Max

First method:

1. Turn off the phone by holding the Power key.
   
2. Afterwards hold and press Volume Down + Power button until you see Bootloader menu.
   
3. Then form the menu choose option "FACTORY RESET" using Volume Down to scroll, and Power button to accept options.
   
4. Now wait until your phone reboots.

Second method:

1. Turn on the phone by using the Power button. 
2. Afterwards go to Settings and then to Backup & reset.
3. Tap Reset Phone. 
4. Choose Erase All Data if you are sure you want to clear all your data. 
5. Select OK to confirm the whole operation.
6. Good job!