Remove the plugs on the bottomrail to release the string ladders. This will reveal the knotted lift cord. Undo the knot and pull up the lift cord enough to release the slats you need to remove.
Remove the bottomrail and slats necessary to shorten the blind.
Determine the desired length, then insert the bottomrail into the last ladder rung.
Cut the string ladder above the rung that hangs below the bottomrail. Be sure that you have enough ladder hanging to be able to insert these strings into the route holes on the bottom of the bottomrail.
Insert each of the lift cords through the bottomrail hole and tie a knot. Make sure that the lift cords are even and that the bottomrail hangs straight.
Adjust to the desired length by lowering or raising the knot in the lift cord. You may also insert more or less of the ladders in the bottomrail route. DO NOT try to adjust the length by pulling on the lift cord.
Replace the bottomrail plugs. Use a rubber mallet or hammer to keep from marking the plug.