How do I download Yosemite on my imac?
Check your iMac model and the date.
In About this Mac (here is mine)

Yosemite requires iMac (Mid 2007 or newer)
Log in App Store and get it from there. The download process can take very long time, a hour or more (it is &gt; 5 Gig file), depending on your Internet speed.
Once it is done, find the file called &quot;Install OS X Yosemite.app&quot; and click on it.
If Yosemite does not work for you then get the 10.7.5 (minimum required) for TurboTax 2014.