I'm pretty sure that, the last thing you uploaded is what the featured item is.

However, you can make a folder and drop something that you want to be a featured item into it. However, there is still no "feature this image" function here.

Go to Settings, then from there go to Submission Folders under the "Preferences" column.

Then from there, click on any of the folders under "Edit Folder Options" (these are ones you already made) to modify the folder's individual settings. There should be a box right there that you can check or uncheck that says "This is a featured submission folder." That way you can have folders that will show up under the "Featured" section and you'll have ones hidden away. You could even make it so certain folders don't show up anything in them in your submission page if you so choose.