How to change themes in GNOME 3

Hi,

How do I change the theme in GNOME 3? I have looked everywhere and have not been able to find a way.

Any help will be greatly appriciated.

Hi
Install gnome-tweak-tool.

Thank you for your response. GNOME Tweak Tool looks like what I want, but under shell theme it says User extensions not enabled. How do I fix this?