Restoring Original Firmware on WRT1900AC

A couple years ago I installed Luci onto my WRT1900AC because I was curious at the time. Now I am wanting to turn my router back to its original factory firmware and I can't seem to find any help. Thanks!

It says "sysupgrade must be forced using the command line" and doesn't explain any further. Can you elaborate a bit for me.

Look further down at "CLI".

alright, I have Putty downloaded. I don't see where to access the terminal and what image links I am supposed to include

Chose the correct image link for your version.