for a lifting fret on my jackson I did this:
First, put a piece of wood on top of the fret, and use a hammer to GENTLY tap it into place. the piece of wood acts as a "buffer" between the fret and the wood. Do NOT just hit the fret with a hammer, as it will leave a nasty dent. If this doesn't work then:
1) put tape on the fretboard on both sides of the loose fret so that the glue will not mess your fretboard up
2) put some superglue on each side of the fretwire so that it seeps under where the fret is lifting up.
3) press the fret down and hold it firmly until the glue is set.
That should fix it.