Sorted this - for anyone else that would like to get rid of the radio buttons (or bullets), right click the page and go to "Web page properties". Click on "HTML code (head)" and paste the following:

<style type="text/css">
.theme-default .nivo-controlNav a {
display:none
}
</style>

This seems to overide the settings in default.css. You can also get rid of the hover arrows by pasting:

.theme-default .nivo-directionNav a {
display:none
}

Hope this helps someone - and thanks again for all the advice.