Thanks so much @fiddlinsteudel for that advice. The last weeks I've really tried to find a way to play faster but with my wrist being stiff, it's so hard. I got a bit stuck with this... So, I'm very grateful for these tips. I especially liked the first two videos because they focus on the right hand flexibility. The others focus more on the left hand. Today I'm going to start practicing with the tips from this videos and I hope it will soon be easier to play fast. Thanks again!