Here's what my site pretty much looked like before I uploaded my own images:
In order to upload your files, you need to click the HTML/CSS button (I circled it in yellow below) on the Design tab.
Also, when uploading your files, make sure they have the same names as the files you're replacing, otherwise, your site will still look the same as the template.
I hope that helps, you can always contact weebly with questions or me if you'd like.
Before I finish, I want to point out the ability to use paypal, I'm not selling anything on this site in particular, but I'm thinking of selling some of my creations, so I tested out the feature and it's so accessible. I just put my paypal email address in the settings and it automatically linked my account with the paypal element I dragged from "Revenue" on the Elements tab.
This blog feature is also pretty cool. Weebly, you're fantastic, thank you.