well... depends... what type of acoustic guitar you have... on some ofthem you can put a piece of cardboard under the strings by where the bridge is and that would work...
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If you are looking to lower it, you can sand down the saddle. If you are looking to raise it, you'll have to buy a new saddle and start over again.

www.frets.com <---- acoustic guitar bible. check out the article on adjusting action at the saddle.

EDIT: ^ That is a very poor way to do it. You deaden the sound when you do that, as the vibrations do not transfer as well through cardboard as they do through bone or even plastic saddles.

Partscaster/Tele into a bunch of pedals, a Maz 18 head, and a Z Best cab.
If your looking to lower it I sanded down the saddle doing what frets.com said. I just took it slow and it worked out.