Builder Image Upload Hanging

I am in Upfront Builder - Using the Spirit Theme.
I have opened the background for the Home Header on the Home Page.
I have selected the preferences (green cog).
The background type is image and the image type is full width and I have selected Browse...
I selected a photo that is 843kb jpg 3264 * 2448 and then open.
It took a while but it loaded ok.
Now I want to change it for a different photo.
I do exactly the same thing with a photo that is 2448 * 2448 and 2.4mb and it just hangs on uploading.