If you're already on El Capitan you can update from the Mac App Store. Apple says a download will be coming soon to the link below.
This is a pre-release update to OS X v10.11. If you have OS X v10.11 installed, download this update by clicking Updates in the toolbar of the Mac App Store. If you do not have OS X 10.11 installed, use your download code on the Mac App Store to get started.