If you have your phone unblocked and rooted should not be difficult with the app Flashify. It's how I flashed my TWRP. I don't know if someone have a video. I went through this one:
https://www.youtube.com/watch?t=45&v=hjbWUTqqWb8 (it's about flashing a ROM and the TWRP - just skip the ROM part). Not sure if this applies to you though...! choose wisely...!
I'am using the TWRP from TeamWin 2.8.7.0 NOT the one from the video. The process is exactly the same.