Strings are very far away from the last frets on...

Question

my son has an epiphone "dr" acoustic guitar. loves it except for the space between the strings and last frets on neck (hard to press strings down on those frets). was told to sand down part of bridge to bring strings closer to neck....but we spotted an allen wrench nut just inside the sound hole that is just underneath where the neck connects to the body. what does this nut do? would adjusting the nut help solve our problem?nick fray