Custom 4

According to Macromedia Fireworks MX, this image is 500 pixels wide by 418 pixels high (6.944" X 5.806") with a resolution of 72 pixels/inch.

If I try to upload it to a fulfillment site, the image will be too small or too pixelated or too fuzzy.

What do I do?  How do I convert it to an image which is suitable for printing on a t-shirt?