Upload logo file during install script

Hello,

As part of a custom install script, I need to prompt for a logo file upload. Once the file is uploaded, I would move the uploaded file the correct path for the site's logo. I have found the "ui_upload" function, which looks like it should work. I understand how to add the "ui_upload" to the form. I don't understand how the file should upload, once the form is submitted. Can anyone offer any tips or good documentation?

Thanks for any help.