Major upgrade to a product (not backward compatible) - new product or update

I am coding new version for a product, but the changes in the code are so drastic that it makes me wonder if I should submit it as a new product or provide it as upgrade to the current one.
The new version is not backward compatible and I don’t actually think that I can make it compatible due to the quite big amount of changes and some new features. I know it will be easier for the users to receive the notification for the new version once its approved, but I know I will receive a lot f support tickets because it may look like a brand new product.

Please advice.

Does it just look new or does it also function new? I’d try to upload it as an update, if the product is well-established and has a fame already and a few hundred sales. Create a script that upgrades the old settings to the new product, and also a frontend script that guides the user through the changes. Photoshop v3 didn’t look like CC 2015, yes it’s the same software and people got used to the new things.