How do i update my macbook pro from OS X 10.9.5...

How do i update my macbook pro from OS X 10.9.5 to 10.10

If you’re able to use El Capitan, Sierra, or High Sierra, upgrade to that version instead.

If you specifically need Yosemite, log into the Mac App Store with an Apple ID previously used to download it, or go to a physical Apple Store and ask for it.