mixed content errors (http:// & https://)

We added an SSL to the site last week and now Google maps aren't loading. E.g. https://www.nzpropertiesonline.com/properties/sunny-seaside-sensation/ If you scroll down and click on the maps tab you'll see what I mean.

The maps are being called over http:// but the page is https://, so I need to ensure that the map URLs and assets get loaded over https:// instead. But I’m not sure where or how to do this. Are you able to help?