To adjust your seat height, start off by loosening the bolt or quick release where the seatpost slides into the frame.
Pulling up or pushing down while twisting is the best way to raise or lower the post. Be sure to tighten the bolt or quick release after making adjustments.
While sitting on your saddle, rotate your pedal so it is at 6 o'clock or at the bottom of the rotation. With the ball of your foot on the peddle, you should have just a slight bend at your knee. if your leg is too straight, lower your seatpost. If your leg is too bent, you should raise it.
Having the right sear height is a simple way to make your ride more enjoyable, improve your pedalling efficiency, and to avoid injuries.