I'm relatively new to Drupal and Ubercart and have a question about theming.

I have created a store using Ubercart and have themed it. However, I think that I went about theming it the wrong way and was hoping you could provide me with some links/info that can help. Currently, all my theming was done inside the Ubercart module rather than in my them. For example, if when I wanted to theme the cart block I went into uc_cart.module and changed the:
function theme_uc_cart_block_content(...)
{
...
}

Is there a way I can do this from within my theme rather than having to change the .module code. As you can imagine it's now somewhat painful for me to update the Ubercart modules because I might lose my theme changes.

Thanks for the help!