When the site was created it also created a folder structure inside sets which you can add images to. One of the ideas behind DPG sites is that they are very easy to update. We think you should be able to spend some time setting up your site and then updating it in the future will be as easy as adding images to sets.
You can add images directly to a set.
Using sets with the website
You can also create sets within the website page sets to help you organise your images. This site shows an example of sets in use.