to commonly asked questions.

Can I go from Snow Leopard to El Capitan?

Can I go from 10.6.8 to 10.11?

Yes. Apple allows a jump that large but you can't jump from 10.6 to 10.12 or higher. Also, 10. does have to be completely up to date first as well. (10.6.8) However, if you've not previously downloaded 10.11 from the App Store, Apple doesn't make older operating systems available. Still possible. You just have to obtain a copy of the prior operating system.
This image is a theme.plist hack