The simplest way is generally to unlock the bootloader (information at HTCdev.com), flash a custom recovery, then flash a superuser package. I'm not being more specific since that last has moved on a bit since I last did it so I'd be a bit out of date.
A custom recovery (e.g. TWRP) must be built for the specific model. Do not attempt to flash a recovery intended for a different phone. You use fastboot to flash it, installing that is described in the bootloader unlocking procedure.
Unlocking the bootloader will factory reset the phone, so back everything up first.
Don't waste time with rooting apps, the exploits they use have been closed in recent Android versions. That's probably why you were having no luck.