Go to OSX Daily to read How to Change Refresh Rate on Mac Displays
Changing the refresh rate of a display can be needed by some Mac users, particularly if they work with movie files and video editing. Generally speaking, most users should keep their displays set to the default refresh rate for their particular screen, but if you need to adjust refresh rate you’ll find it’s simple to do so with displays used on the Mac.
It’s important to note that not all Mac displays can change their fresh rate, though many third party external screens offer different refresh rate options. In fact, most Mac internal screens can not…
Read more: How to Change Refresh Rate on Mac Displays