Develop a short module on a web application

I have an web application, in which user can design a tshirt by draging and droping some icons over the tshirt. And after designing the tshirt with icons, the application generates a png file from the canvas html. Now I want to print the png file onto the selected tshirt. But problem is the generated png file is too small to print. For printing it requires either 300dpi image or any hi res. image. So my requirement is, either convert the png file into svg file on the fly or generate a bigger version of the png file. The Tshirt Design application is developed in HTML, Jquery, PHP.