Erin,
Are you switching domains?
If not, just make sure your munchkin code is embedded on the new site code. You may have to adjust any website visit triggers if URLs were changed.
If you have a new DOMAIN, then you will need to change the CNAME for the marketo LPs and possibly talk with support. Existing pages will need a 301 redirect to the new site. That might be tedious to setup, so speak to support.