Within a Value Proposition you can download into PowerPoint by clicking the More button and selecting Export from the menu (see red outline below). This will open a dialog box with one or more versions. To export, simply click the link and the download will begin immediately. When done, PowerPoint will open.
Be sure to Save any changes to your copy of the Value Proposition (called a Unique Value Proposition) before you export.
An alternate way to download is from the Sales Home page. First, click the Search filter to show "My Unique Value Propositions." The click the Actions button and click Export.