You will need:
Headphones with a wire running to both halves - NOT the kind with just one wire
A jeweler's screwdriver that fits your screws - If your headphones don't have screws, exchange the screwdriver for a hacksaw
That's it. First, how to remove the bar with screws.
Find the size jeweler's screwdriver that fits the screws in the headphones, and remove them. Pull each 'phone out of the bar, so that the headphones are now in three pieces. Discard the bar and screws and you're finished! Enjoy your new Head-Buds - or is it Ear-Phones? You decide.
I'll try to explain how to remove the bar from headphones without screws as best I can.
Measure how far out you need to cut the bar. Place the headphones around your head, and pinch with your fingers the spot where the bar stops touching your ear. While still holding the spot, remove the 'phones from your head and cut the bar at that spot. Repeat on the other side. Be sure to clean any plastic shavings that you may have produced and discard the bar. You're finished! Enjoy your new Head-Buds - or is it Ear-Phones? You decide.