I cannot remove light cover on ceiling fan to replace globe

There are usually small screws around the outside of the globe that screw into a recess on the globe with a rubber ring around it to keep the screws from hitting the glass.

If it is a fan/light without obvious screws, look around the perimeter of the globe...if you see multiple sets of dimples (usually three sets total spaced evenly around the perimeter) you may have a threaded globe; which means you will have too unscrew the globe. If the whole light fixture rotates with the globe, then it may be mis-threaded. Provide counter-pressure to the [metal] base as you rotate the globe. Do not try to pry it with a tool (like a screwdriver) as it will most likely cause the glass to crack or shatter.