Q: mac os x 10.6

Mac OS X 10.6.8 Update Combo v.1.1 - http://support.apple.com/kb/DL1399

Are you trying to update 10.6 or upgrade your OS version to El Capitan?

Check that your computer is compatible with Mountain Lion/Mavericks/Yosemite/El Capitan.

To check the model number hold down the option/alt key, go to the Apple menu and select System Information.

      MacBook Pro (Mid/Late 2007 or newer) model number 3,1 or higher

Your Mac needs:

      OS X v10.6.8 or OS X Lion already installed

      2 GB or more of memory (More is better - 4 GB minimum seems to be the consensus)

      8 GB or more of available space

Check to make sure your applications are compatible. PowerPC applications are no longer supported after 10.6.      

Application Compatibility

Applications Compatibility (2)

El Capitan 10.11 Compatibility information

Do a backup before installing, preferable 2 backups on 2 different drives.