It's not uncommon for a heat sink to become screwed on too tightly, making it difficult to remove. If this is the case, there are a few things you can do to loosen the screw.
First, try using a heat gun or hair dryer to heat up the area around the screw. This will often loosen the adhesive that is holding the screw in place.
If that doesn't work, you can try using a pair of pliers or a wrench to loosen the screw. Be careful not to damage the heat sink or the screw in the process.
Once the screw is loose, you should be able to remove it by hand. If it is still stuck, you can try using a screwdriver to gently pry it out.
Once the screw is out, you can remove the heat sink by gently pulling it away from the CPU. Be careful not to damage the CPU in the process.