Can I edit pre-built template modules?

I am using one of Marketo's pre-built templates "Iceberg" to create emails with and I was trying to edit certain modules and seem unable to:

1. In the Sponsors Module - I am trying to delete the set of 3 sponsor logos all together and can only clear content, not delete their containers
2. In the Social Module - I only want to show certain icons, but I cannot seem to delete the ones that we do not use
3. In the Call to Action Module - I would like to make the button rectangular and not rounded, can't seem to find a way to do this

Thanks in advance for any advice about these items!