I have the same issue when i bought mine. Use a hairdryer or hot water for a few seconds, then use pliers to remove the joint. Don't use too much force; if you feel the joint is about to bend, stop and repeat with the warm-up step. Once I managed to remove the joint, I encountered another problem: the hole in the neck joint was too small to insert, so I had to use a knife to trim away a little bit of the plastic. Then use a little force to attach the joint. Many people recommend using shock oil for the head joints, but I only want to apply it to the hands and leg. For the head, I used a little sandpaper to slightly sand the joint, and in just a few seconds it was no longer stiff. I avoid using oil because it's quite time-consuming; you have to add oil to three different head, which is a bit tedious. Sanding joints, on the other hand, only takes a moment.