One of the simplest ways to do this (assuming you do not want to use an audio
editor), is to use the freebie, "mp3DirectCut" mp3 file cutter to cut or
split the file, all of which it does WITHOUT having to reencode the mp3
file. it is not an audio editor; it is just a splitter or cutter, so it
does not reencode the file (which is an advantage).
it is made by the same guy who makes that excellent, lightweight, directory
music player, "1by1". (Emphasis on "file directory" music player, as
opposed to a "playlist" player (which I cannot stand dealing with :-)
Here is the link for mp3DirectCut.