Upgrading from Yosemite to El Capitan, but not Sierra We have an older iMac (Model A1311, Mid 2011). It has been running Yosemite. We have run into some of the WIFI issues associated with Yosemite. 

Is it possible to upgrade to El Capitan but not Sierra? 

El Cap has been out longer. Its my wife's computer, its older, and I really don't want to be debugging Sierra until a few  more "dot" releases come out.
You don't have to upgrade to macOS Sierra if you don't want to.
Already &quot;Own&quot; El Capitan
If you have already &quot;purchased&quot; El Capitan, then it will show up under the &quot;Purchased&quot; tab of the App Store.  By &quot;purchased&quot; I mean the &quot;free download&quot; that Apple provided.

Download from the AppStore
Per Apple Support, you can download El Capitan directly from the AppStore

Go to an Apple Store
If you still can't download, you can take a visit to an Apple Store near you, or you could have a friend download it (if they already purchased it) and make a USB installer.