Where do you find the default Index fill factor and how to change it?

The easiest way to find and change the default fill factor value is from Management Studio, right-click the SQL Server and choose properties. In the Server Properties, choose Database Settings, you should see the default fill factor value in the top section. You can change to a desired value there and click OK to save the changes.
 The other option of viewing and changing this value is using sp_configure.