First off, when you say it's one high fret, is it a fret that has visibly lifted slightly i.e. you can see a little gap between it and the fret board? If you can't actually see it with the naked eye, you can check by attempting to slide a thin piece of paper in there. Assuming there is a gap, then a smart tap with a small hammer will probably be all that's needed.
If a levelling is required and it is only one fret, then a sharpie pen, sand paper, emery board (nail file), 120, 240, 320 and 400 grit paper, masking tape, should be all you need.
Drop me a pm if you want any DIY instructions.