In what section of Studio can users upload and manage ad files?
- Dynamic Content
After you’ve added a creative, continue to the Manage Files screen and upload the files that power your ad. You can also add files already uploaded to the “Assets” tab to your creative. If you upload multiple image files, the first one is automatically assigned as the backup image. 1 GB is the default total size limit in Studio.
Read more here: https://support.google.com/richmedia/answer/2453425