How to raise the handlebars on a mountain bike with a threadless stem?

To raise the handlebars on a mountain bike with a threadless stem, first loosen the bolts on the stem cap using an Allen key. Then, loosen the bolts on the side of the stem that clamp it to the fork steerer tube. Adjust the stem to the desired height and make sure it is aligned properly with the front wheel. Tighten the bolts securely and test the handlebars to ensure they are stable before riding.