If it is in good health, you can make a cut at a shallow angle, to allow rain to drain off, and immediately seal it with grafting wax, to keep the wound from drying out too much, and too much of a stub forming. That also helps keep out disease organisms.
Several new crowns will sprout from the stub, and should be thinned to the best two or three, for good shaping. New crowns may also appear from near ground level, or just below, and might be harvested for new plants, if they grow their own roots.
Note that the 5 feet that you remove will be replaced in just a few years, and you will be back to where you were with the height. What is the reason for shortening it?