How do I remove a screened on number from a shirt?

I play on a sports team, and I received a practice jersey and practice t-shirt. The jersey is polyester, and the t-shirt is 50% cotton and 50% polyester. In both cases, the number is screened on as 13, and my number is 31. How do I take off the numbers and replace them with the right ones, and where can I go to get this done. They both seem like they are not completely ingrained, and can be taken off. Any solutions? I live in the Es county area of New Jersey, so if anybody knows any shops of this capacity it would be appreciated.