The Folders by Category and Files by Category pages will display a custom view option. The custom view option provides an easy way to use a filter to drill down to very specific types of files or folders.
When you click on the Custom View under the Files by Category section you will see the filters that can be used, shown below.
These filters let you choose the specific files you want to see. You can use one filter or combine multiple to further drill down. After you click Apply Filter you will see the files that match the given filter. You may also bookmark the page to come back to a specific filter in the future.
The custom view for folders is very similar to the custom view for files but the filters are not identical. Below is an image showing the options available for the custom view for folders.
Once you drill down to the specific types of files you are after, you can review the files and optionally delete what you no longer need.