If you wish to flash your phone himself you will need to collect some important things.
- Download and install the latest setup of your flashing tool or box which you want to use as a flasher
- After that download latest flash files of your phone
- If you are going to flash your phone with tools just connect your mobile with your PC via compatible USB data cable
- If your PC is not detecting your phone you will need to download and install latest USB driver of your mobile
You can download latest stock firmware of HTC One M9 from below download links. The download links are tested and good working. You can update your mobile firmware any time any where if you have an internet connection. During updating your phone will be connected to its official server and will find new updates if it has been released by its developers.
HTC One M9 Stock ROM