If you are talking about the text labels for the radio buttons, they're not really part of the radio button and so there's no radio button attribute to change.
What you can do (modern browsers only) is the place the labels in span tags, give them an id, and then change the contents of the span.
and in the script
Is that what you were after?
document.getElementById( 'radioLabel1' ).innerHTML = 'something new!';
If you also need to change the values that get submitted with the form for the radio group, that can be done as well...