You can hide, crop, upload, and replace a photo. There are two ways to do this:
Hover over a photo on a page in Preview and all the options available to change the photo will be highlighted.
Alternatively, click the Edit button below the page to access the page edit. Here, you can select the photos you want to manage: hide, return, rearrange, and upload more photos. Once you have made your changes, click Apply to rebuild the page.
To upload the photo, go to the How do I upload my photos page.