I understand - you're pretty new to this device and maybe to HTC's write protection they invented last year. That's ok mate.
With TWRP installed it's a very simple thing to flash the new kernel. Did you already do some flashing on these devices? I think it's more complicated to get root the first time than flashing a zip from TWRP.
Anyway I'll help you there. Simply download Flars kernel and copy the zip-file to your internal SD-card. Boot into TWRP and choose the install option. Navigate to your internal SD and select that zip file. Start flashing and choose simply the defaults you get offered by the aroma installer. Finish, reboot and the write protection is gone. TB will work as always.