Outer Foil: Squeeze the old outer foil release buttons and lift the out foil upward to remove it. To insert the new outer foil press down until it snaps into place. Inner Blade: Remove the old inner blades one at a time by grasping them firmly at both ends and pulling straight away from the shaver. To insert the new inner blades, hold the blades one at a time at both ends and press downward until they snap into the shaver. It is recommended that you replace the outer foil at least every year and the inner blade(s) at least every two years to maintain your shaver's cutting performance.