Well, first, to increase the size of the image go to Image->Image Size.
Then, to change the pixel aspect ratio, go to Image->Pixel Aspect Ratio and set it to what you need.
Of course, because you’re changing the proportions of the pixel, and you’re changing the size of the image, you’re going to get some blurring and distortion. The distortion can be dealt with using the Edit->Transform tools, and you can somewhat see to any possible blurring with an unsharp mask or other sharpen filter.
However, for best results, always see to it that your pixel aspect ratio and size are set properly before starting. I assume you didn’t have this option as you were using a template, but keep that in mind if you ever decide to make something from scratch in Photoshop.
Hope this helps,
Twitch