I am using MacBook Pro running El Capitan. How should I upgrade LO, which URL is best to use?

I’m not a tech expert, so please give fully detailed info.
Am I supposed to QUIT all LibreOffice documents before I begin the update?

Yes, when performing an update, all documents should be closed.

Downlaod here: https://www.libreoffice.org/

Installation Instructions here: Installation Instructions | LibreOffice - Free Office Suite - Based on OpenOffice - Compatible with Microsoft

Hi ebot, The installation instructions page you noted for help doesn’t say anything about how to proceed when using a Mac, and I don’t want to make a mistake, so some additional guidance would really be appreciated. Also, is it important to quit out of LO before doing the upgrade? Thanks for your help.

Yes, when performing an update, all documents should be closed.

Sorry, I myself use Win-10 and can not help specifically to the Mac, unfortunately. Maybe another user can help you with a Mac system.
Alternatively, you can also sign up on the users mailing list and put your question there again concretely. I wish you success.
Mailing lists: Mailing Lists | LibreOffice - Free Office Suite - Based on OpenOffice - Compatible with Microsoft