If you look at the system requirements for the update....you will see that it will update through 10.9....Yosemite is a 10.10....I just made the same mistake
I just found this....and it works....and it's legit.
1. Reboot computer or use Activity Monitor to force quit any prior Adobe Flash installation process that may be still running
2. Download Adobe Flash update using this link (assuming you are using Safari or Firefox): Flash Player for Safari and Firefox - NPAPI
3. Mount flash player by clicking on flash drive icon on desktop
4. Right click on Flash file
5. Choose 'Show Package Contents'
6. Open 'Contents' then 'Resources'
7. Run file 'Adobe Flash Player.pkg'
8. Reboot computer.