Possible to use radio buttons instead of checkboxes?

The Simplenews Multiple Signup Block is a great concept and I've installed it and it's working well.

Here is my question: In the block itself, is it possible to change the input type from checkbox to radio button? I've attached a screenshot of what I'm talking about. I'm not a programmer but if this is a fairly simple fix, I can probably tinker around and change a little bit of code, if someone can just point me to the applicable files. Thank you