You pretty much do the same thing, but just make a "sights2" folder as a backup and then place your old ones there or simply rename it.
Then make a "sights" folder and place the downloaded content there.
ALSO!: Put the "Default" sight from the ORIGINAL folder (or copy it) into the new folder. (This is for buff gunner sights etc. that you won't change.)Once you've done this you will need to change all of the gun sights on your planes in-game through the in-game option on the clip board.