In order to bend a note on a guitar with a fixed bridge, you can merely push the fretted string towards the center of the neck with your fretting finger(s). In order to bend an open note, the player can push on the string from behind the nut. In both cases, the string is stretched by the player. This has the same effect as turning a tuning peg up. That is, the pitch of the note rises.

Most times that a player bends, they usually bend the note up either 1/2 step or a full step. The bending of the body and neck of the guitar away from the player would lessen the string tension and lower the note, but possibly wreck the instrument. It might be advisable to get a similar yet less damaging effect by sliding down a few frets and either using a vibrato technique or bending.