Unable to change the image in construction mode

I put an image in, not realising the wording obstructs the face. I flipped the image offline, and uploaded that, but it has not changed. I tried uploading another image, no change. I permanently deleted all three images. It is still showing the original image.

Presumably this is a server caching feature… how do I clear the cache so that I can get the under construction page looking like I want it to?