i can't upgrade to OS X 10.11.4

You may take a look at this --> How to upgrade to OS X El Capitan - Apple Support

Check compatibility

You can upgrade to OS X El Capitan from OS X Snow Leopard or later on any of the following Mac models. Your Mac also needs at least 2GB of memory and 8.8GB of available storage space.

MacBook introduced in 2009 or later, plus MacBook (13-inch, Aluminum, Late 2008)

MacBook Air introduced in late 2008 or later

MacBook Pro introduced in mid 2007 or later

Mac mini introduced in early 2009 or later

iMac introduced in mid 2007 or later

Mac Pro introduced in early 2008 or later

Xserve models introduced in early 2009

To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu . If your Mac isn't compatible with OS X El Capitan, the installer will let you know.