Turn the chainsaw off by pressing the power button on the side of the saw. Make sure that the saw is completely turned off before you start the replacement.
Loosen the screw on the right side of the blade to loosen the chain. Pull the blade out of the chainsaw's crankcase. Pull the old chain off of the blade.
Put your new chain on the blade so the sharp teeth are facing out. Put the blade back into the crankcase and then replace the screw holding the blade in place.
Tighten the screw so the blade is secure to finish the installation.