You can do that from here:
Monitor > Maps > Choose Map > Pulldown and choose "Edit Campus" > Import new image.
If you want to go back to the google map I would recommend that you go to the same path above and do not choose an image and choose next. Copy the dimensions of the existing googlemap image and use this same dimension when you import the new image. If you do not and a new size is chosen you will not be able to add the image back if needed since there will be a position conflict with any placed buildings.
As always I would backup prior to making these changes.
I tested in my lab and it worked fine changing it and then going back.