You can add the scaling option to the src part of your html code. The smaller the number, the further you increase. Zoom = 10 is a good place to start testing.
<iframe width="600" height="450" frameborder="0" style="border:0" src="https://www.google.com/maps/embed/v1/place?key=API_KEY&q=Space+Needle,Seattle+WA&zoom=10"></iframe>
Google " ".
https://developers.google.com/maps/documentation/embed/guide