Update it in the normal way in iWeb and then publish to a local folder and upload the new pages - you don't need to upload the whole website again, just the blog pages and the files that go with it.
If you are using iWeb 08, thne you'll need to publish to a local folder and use something like Cyberduck or Yummy ftp to upload to your server.
You are aware that by publishing an iWeb blog to a 3rd party FTP server you will lose the following features, right?
Features Unavailable When Publishing to a 3rd Party Server:
◼ Password protection
◼ Blog and photo comments
◼ Blog search
◼ Hit counter
I have tried to update my iWeb site for the first time since installing Lion, moving to iCloud and using freeola to host the site. Everything seems to work ok, but the blog hasn't updated. Does anyone know why this might be?