How to change default search engine in Microsoft Edge browser?

As of now, Bing will be the only search engine for Microsoft Edge. You have no option to change it.
However, it looks like this option will be available, because as per the reports - there is an option button for the purpose, but greyed out. Maybe Microsoft will come up with the option in the subsequent builds.

This has since changed.

http://windows.microsoft.com/en-hk/windows-10/change-the-default-search-engine-in-microsoft-edge

Yes! you can change default search engine in Microsoft Edge.
Just follow these steps.

If you want to make google.com as your default search engine, then

1, open www.google.com
2, mark this as favorite (click on the star button in the right end of address bar)

3, Go to settings in edge > 4, View advanced settings

5, search in the address bar with click on the change button.

That's it there you can change.