The page design is all handled through the .css. You can find the line of css that controls the width of the upload field and simply change it. Adding a cancel button would be done by going to Insert->Forms->Button and adding a cancel button. You can copy the style from the other buttons to get it to look the same.
Although you can run the wizard and be done, using Dreamweaver to fully customize what the wizard won't is how to create fully unique forms. If you want, make a list of the customizations you want to do and a url of the page as it stands and I'll tell you what i would do to make those changes.
Our extensions build on top of what Dreamweaver does and don't replace Dreamweaver entirely, so learning how to use the various features in Dreamweaver directly to tweak the result adds to the flexibility of the result.