How do I update the submit button with my own image?

In order to replace the standard gray button with an image, follow these steps:

Within the payment button HTML (button generator), find the following line:

<input type="submit" name="submit" value="Add to Cart">

Replace the line above, with the following code below:

<input type="image" src="http://www.YourWebsite.com/YourImageFolder/YourImage.gif" border="0">