Open a listing to edit by: 

Clicking on the house icon - top right hand corner to open all your listings.

Select the listing from the list or enter the area / street name / reference number in the search field (right hand corner)

When you open a listing in Base you will get this view which provides a summary of every section that you've completed when the listing was captured initially. 

Select the section that you would like to edit by clickin on the icon in the green strip on the right hand side.

For instance: 

You would like to reshuffle the photo order

Click on the photos icon, click on the photo that you would like to reshuffle - drag the photo to the desired position. 

Save your changes.