Q: Upgrade OS X from 10.7.5 to 10.11.5 on EXTERNAL hard drive

I have an old Macbook hard drive from 2010 that was removed and is now functioning as an external drive.  It is running OS X 10.7.5 (Lion) and I was wondering if it was possible to upgrade this directly to 10.11.5 (El Capitan) so that I can keep it in synch with my current Macbook Pro.   Ideally I'd like to keep all of the files contained on the external drive intact so would rather update the OS if possible rather than installing a clean copy of El Capitan on it.

Is this possible?