How do you lower the action on a guitar?
To lower the action on an acoustic guitar you don't have to adjust the bridge in any way, you only have to adjust the saddle. The saddle serves the same purpose as the nut, controlling the height of the guitar strings.
How can you lower the pitch of a guitar string?
So guitarists resort to another way to change a string's pitch — by shortening its effective vibrating length. They do so by fretting — pushing the string against the fretboard so that it vibrates only between the fingered fret (metal wire) and the bridge.