Macbook 4.1 upgrade to OS X 10.11 El Capitan

I have read that it is possible to upgrade a MacBook 4.1, Intel based from OS X 10.6 to 10.11 El Capitan. I have followed the suggestion I found on Support for upgrading a Mac Pro 4.1, also Intel based

Go to Download OS and click on OS X El Capitan 10.11

this downloads InstallMacOSX.dmg to your Downloads folder.

When downloaded open to InstallMacOSX.pkg, double-click on

that and an installation window will open, this does not install El Capitan

but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which 

you will find in your Applications folder, it should be 6.2GBs in size.

However when I tried to open on my MacBook 4.1 InstallMacOSX.pkg i got an Alert telling me "This version of OS x 10.11 cannot be installed on this computer". I had assumed that the procedure would work also on a MacBook 4.1, but I must have been wrong. Is anything else I can do to get OS X 10.11.6? Many thanks. Raffaello