How to Set Default Email Program on Mac

Can you help me? I did the action of this video several years ago. Now I have 5gb of data in my Mac Mail program and 5gb of the same data in my Google mail program. It is using up all my computer space for the same amount of info. How can I removed the Mac mail as the default location? I only want to use the google program.

Cheers, worked perfectly for me, even 9 years later!

Thank You So much

Thanks, man