If you're going from one Kohler shower head to another, the replacement could not be easier. You simply unscrew your existing shower head, and then screw the new showerhead into place.
A new showerhead can also help with water pressure. If you currently have low water pressure and want it to be higher, try replacing the showerhead. Sometimes, this little part can make a big difference.
Shower heads can be found at www.supplyhouse.com