2) If you downloaded it on your computer, rembmer you can send the file via USB / ADB, like so:
$ adb /path/to/file.zip push /sdcard/Download/file.zip
3) Boot into recovery:
$ adb reboot recovery
4) In TWRP, tap Install and navigate to the SuperSU you downloaded and swpie to flash.
5) When prompted, Wipe Dalvik / Cache
I chose to make another backup here and, once booted to a live system, send the backups to Google Drive. That way they’re easy enough to access, but not hogging up space on the phone itself. I also chose to make a backup here so that I have one of completely stock system and a stock + root system.
6) Finally, reboot the system.
Now, continue to Part 4 which will quicly cover flashing ROMs (which is very similar to the steps already covered).