This is a simple explanation for you ... http://www.ehow.com/how_5189790_remo...ower-head.html
I typically remove the head from the threaded coupling. I just look for the restrictor inside the shower head. A 3/16" drill bit is all it takes to puncture the restrictor .... or you can pry it out. Whatever.
I would also check the diverter to see if the spout needs replacing. You can unscrew the spout and get a replacement. After putting teflon tape on the water stub coming out of the wall, screw the new spout in place. If it does not reach, you might need to buy an escutcheon to fit over the stub before screwing the spount into place permanently. Remember to apply silicone liberally to the back side of the escutcheon so you never get water in the wall.