When I'm up as high as I can go, I have potential energy but no kinetic energy. So I can set these equal to each other. Potential energy increases, and kinetic energy is constant. Potential energy increases, and kinetic energy decreases. If I throw a ball in the air, on the way up, the height is increasing but the velocity is decreasing.
Potential energy decreases, and kinetic energy is constant.
An elevator going down at a constant speed. Potential energy decreases, and kinetic energy is constant. Potential energy is constant, and kinetic energy increases. A car accelerating on a flat highway. Potential energy is constant, and kinetic energy is constant.