Depending on your door, you may need to adjust the backset, the distance between the edge of the door and the center of the doorknob. Most doorknobs can accommodate different backsets.
Reverse the removal procedure to install the new doorknob. In most cases the holes for the new doorknob will match your existing holes. Be sure to orient the new striker in the correct direction to ensure that the door will close properly.
Screw the new latch in, setting the screws by hand first and then tightening them with a power drill. Set the doorknobs in place, set the screws by hand, and then tighten. Don't over-tighten the screws or you'll bind the doorknob.
Test the new handle to make sure it turns and locks properly.