PowerPoint will automatically save a new presentation in the new format. You can see what format your file is being saved in by looking at the Save As dialog box. (Click the Microsoft Office Button , and on the menu, click Save As.)
In the Save As dialog box, look at the Save as type box: The new file format is there by default. It's called PowerPoint Presentation. (In earlier versions, it was called Presentation.)
Note If you've set Microsoft Windows to show file name extensions (the letters in the file name that follow the dot), you'll also see the file name extension for the file type, like this: PowerPoint Presentation (*.pptx). That final "x" means this is a PowerPoint 2007 file.
The name of your saved presentation in the new format, including the file extension, would be something like Annual Report.pptx.