It's easy
The only hard part about repacking a stuffing box is the place and position in which you have to work. If it were on a table in front of you, it would seem trivial. Unscrew the adjusting nut all the way. Use one of those cork-screw shaped tools to pull out all of the old stuffing. Make sure to get it all. Cut three wraps of new packing. You can put three wraps around the shaft to size it, cut a stroke or two to mark the locations, and then finish cutting on a board in the galley, instead of upside down. Get back into position, and insert the rings, one at a time, into the box. Push each ring as far back as possible. You will need to use a small screwdriver or similar tool to push the back ring. Each ring should lay flat. If you cut the a piece too long and can't shape it into a ring with ends abutting, you will have to recut it. The cuts for each ring should be spaced around the shaft, at about a third circumference from each other, though the exact spacing isn't critical. Apply teflon grease, and retighten the nut. Adjust it in the water. That is all there is to it. Really, really easy. If you have a few $, spring for the no-drip packing material that West Marine sells, and use it as the middle ring, per instructions. It comes with plenty for several repackings.