In the inspector Position tab go to last Sliding & Visibility section. There you have option to slide up your object. By selecting the footer part and set "Sliding up based on", you can slide the Footer part towards up. So when you go to your Preview mode the footer part will move up if there will be a gap between body and footer. Just try this and i hope it will work for you.
Footers don't slide. They stay positioned at the bottom of the page like they are designed to be. I can't see from your screen shot, what change you want to make, but get the point that you have a gap between the body and the footer.
Key facts about sliding layout objects:
- It's only visible in preview mode and when you print/save as PDF...
- Sliding fields will shrink but not expand.
- All layout objects below and in the same layout part as the slide/resize field need to also be set to slide up and resize.
- Objects in headers and footers will not slide.
- Portals will shrink/slide to fit the number of rows of records, but fields within the portal row will not shrink/slide.
- Fields will slide up only if Top alignment is specified for it and will slide left only if Left alignment is specified.
- Consistent side borders are difficult to achieve with sliding fields.
A trailing grand summary part will close the gap, unlike a footer, but that has it's own limitations so it may or may not be an option here.