:Inside the mounted disk image, you will find a file named InstallMacOSX.pkg . Double-click this to begin a brief installation process.

: Download OS X Yosemite 10.10 directly from Apple's servers.

It is important to clarify a common misconception regarding macOS downloads:

: Your Mac must have at least 2 GB of RAM and 8 GB of available storage . Generally, any Mac that can run Mavericks can run Yosemite.