Describing flight 2

This is your captain speaking. As we climb to 18,000 feet we will rise through some thick clouds. You may experience some turbulence until the clouds are below us. When we are above the clouds, we will continue to increase our altitude to 25,000 feet. At that point we can speed up to our cruising speed. We'll cruise to our destination of Santiago, Chile, in about three hours. We'll descend around 4:00. But if we encounter any more bad weather, we'll have to slow down. Decreasing speed should result in a smoother ride. Enjoy your flight and thank you for flying Andean Airlines.

slow down = to lower speed
descend = to lower altitude
cruise = to maintain a constant speed
climb = to raise altitude
increase/decrease = to raise/make less the amount of something