cant replace home slider images

Hi. Just installed this theme and began customising it. I put 5 images into the home page slider tool and that all worked fine. Now I want to replace a couple of the images as they dont work well. The “remove” links in the admin area don’t do anything and I have tried in several browsers. I removed one image directly from the media library, but the “upload” link doesnt work either so I cant replace it. Any ideas? thx