How do I upgrade from Yosemite to the latest software?

Start by upgrading to El Capitan - How to upgrade to OS X El Capitan, then upgrade to Catalina if your computer meets the requirements - How to upgrade to macOS Catalina.

Which model (and year - eg: MacBook Pro (15-inch, 2016)) is your Mac?

OK. 10.15 Catalina can run on that.

You can access it from https://apps.apple.com/us/app/macos-catalina/id1466841314 using Safari or just do it from the App Store.

See the link I posted: How to upgrade to macOS Catalina. It will tell you how to proceed.

Thank you so very much for all your help, I Was able to download the El Capitan and then the Catalina and it feels great!!!