Windows 8.1 runs IE 11 that has Microsoft Bing as the default Search Provider.
To change that, go to Tools in IE and select "Manage add-ons" as in the following:
As you may notice, Bing is the only Search Provider in IE.
In the Manage Add-ons screen, select "Search Providers" in the left side listing.
At the bottom, you will see "Find more Search Providers ..." hyperlink. Select this link.
You will go to the Add-ons page where you will see a list of various Search Providers that you may add to IE. I just want to add Google.
Double click on Google.
You will go the following screen. Click on Add to Internet Explorer button.
You will see an Add Search Provider screen. If you want to make Google your default Search Provider then select the checkbox.
Select the "Add" button on the preceding screen and you are done.
Now when you use IE search, Google will be your Search Provider.