Steps to  download Mac OS X 10.10:

• On the Dock, click the App Store icon. The App Store will be launched.
• Click Free Upgrade after finding and selecting OS X Yosemite.
• To sign in, enter your Apple ID and password. If you don't already have an Apple ID, click Create Apple ID and follow the on-screen instructions to get one. 
• Your computer will begin downloading Yosemite once you've entered your Apple ID. Depending on the speed of your Internet connection, this could take several minutes or longer.
• After Yosemite has finished downloading, install it by following the on-screen directions.

Read More: How do I repair Microsoft Edge on Windows?