HTC One S is a part of HTCs line up of smartphones that can have their bootloaders unlocked directly through HTC. To root or install a custom ROM you will have to unlock the bootloader first. Follow the steps below to unlock the bootloader and install a custom ROM

Credit goes to torxx at XDA for the following steps

Step 1: Unlock

Register at htcdev.comUnlock your bootloaderhereChoose your phone from the list

Step 2: Recovery

Download the Android SDKDownload the Interim CWM Touch Recovery of PaulorOfficial CWM of koush (HTC One S)Place the CWM File where the fastboot.exe is (Downloaded with the SDK)Now open the cmd and navigate to the folder where the CWM File is locatedNow type:fastboot flash recovery name_of_the_recovery.img

For Paul's:

fastboot flash recovery r2-modaco-recovery-clockwork-touch-ville.img

Step 3: Root

Now root your phone with SuperSU by Chainfire, thanks a lot!Download SuperSUFlash it with the Recovery:Power off your device and then hold the VOL DOWN + Power to boot into the BootloaderNavigate with VOL and Power to RecoveryNow flash the .zip:- install zip from sdcard

- choose zip from sdcard

- select the CWN-SuperSU-v0.87.zip file and flash it

- Reboot now