Begin by removing the screws holding the doorknob in place. The screws will be located on the interior side of the door.
If your doorknob has screws on the cover plates, remove those to loosen the old knob. If not, look for a small slot with a metal piece on the side of the handle. Then use a clip or the key from the new doorknob to push in on the metal piece as show in the image. That should make the doorknob pop loose.
Pull off the doorknob to reveal the plate below. Look for a slot in the plate along the seam where it butts against the door. Wedge a flathead screwdriver in the slot and then give the plate a half twist to pop it off.
With plate removed, you'll see the screws you should remove with a power drill (Image 1). Remove the old latch by taking out the screws with a power drill or screwdriver (Image 2).
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.