No, you do not have to delete the webpages you published with iWeb.
As long as you do not name the sandvox pages the same as the iWeb ones.
The only file that will be overwritten is the index.html file that redirects to your current iWeb pages.
And now that you use a new application, it's time to say goodbye and proceed to the Sandvox Help pages and forum :
I too have changed from iWeb to Sandvox and using HE for hosting.
I have NOT been successful in getting Sandvox to publish directly to HE.
I am first exporting to a file then uploading with Cyberduck. This is frustrating and time wasting.
Could you assist me with how you succeeded with directly publishing to HE using Sandvox.
Thank you for the assistance
(Sorry for posting in iWeb discussions)