Take the strings, tailpiece, bridge and armrest off.
Loosen the head tension screws and unhook the hooks.
Take off the tension hoop (that's the ring that lies on top of the head keeping it in place
Remove the old head. If the old head has a good mounting hoop, you might want to keep it to use with a natural skin later.
Put the new head in place.
Put the tension hoop back on.
Hook the hooks over the tension hoop and tighten the head tuners until the head is securey fixed in place. Try to get as even a tension as possible all around the rim.
Remount the tailpiece and the armrest. Don't fit the strings and bridge yet, though. We have to tune the head properly first.

Get a piece of cured goat- or calfskin big enough to fit the banjo with plenty to spare.
Soak the skin in water overnight to soften it.
Take the strings, tailpiece, bridge and armrest off.
Loosen the head tension screws and unhook the hooks.
Take off the tension hoop (that's the ring that lies on top of the head keeping it in place
Remove the old head. If the old head has a good mounting hoop, you can reuse it for the new head. If not, you'll have to get one made:
1. Get a piece of thick (3-5 mm - .1-.2") steel wire.
2. Fit the wire exactly around the outside of the banjo pot. You can leave a few millimeters gap between the wire ends.
Stretch the skin across the banjo.
Place the mounting hoop around pot outside the skin.
Put the tension hoop on top, securing the skin safely between it and the mounting hoop.
Leave it to dry overnight.
Trim off superfluous skin.
Put the tension hoop back on.
Hook the hooks over the tension hoop and tighten the head tuners until the head is securely fixed in place. Try to get as even a tension as possible all around the rim.
Remount the tailpiece and the armrest. Don't fit the strings and bridge yet, though. We have to tune the head properly first. It may take several days to tune a new skin head properly since we'll have to do it carefully step by step.