Try not to tear the heat sink sticker, as you'll reuse it during reassembly.

Slide the tip of an opening pick under one edge of the heat sink sticker.

Peel the sticker up until you can grab it with your fingers.

Gently remove the sticker from the heat sink and fan.

During reassembly, place the sticker back in its original location. The residual adhesive should stick well.

If the residual adhesive isn't sticky anymore, tape the outside edges of the sticker to the heat sink and fan with small strips of tape.