Should be a slight twist counterclockwise, then pull down. If the entire fixture is turning, you may need someone to hold the metallic base while you turn the globe.

Thank you Normel! I'll try this tomorrow when there is better light.

I agree with normel. I will just point out that it may also help to push up a little with modest pressure as you turn it.

Very good point! Thanks. I will try that tomorrow when there is more light and I can see.