Need Help!

[KyleRayner]

Does anyone know how to increase the size of a T-shirt design. Someone did great designs for me, but when I went onto Cafe Press to put them on t-shirts, they weren't big enough and Cafe Press will only let me maximum the size to a certain extent. It just doesn't fill up the t-shirt very well.

If anyone can help me, I would be most grateful. I'm not much of a techie!