Help! I have level IV Copperhead but I want Fortune Hunter!
 

I have a level IV copperhead war galleon that I'm very proud of but upon looking at all of the different possible upgrades on pirates wiki I decided I wanted the fortune hunter upgrade instead. Is there any way I can downgrade enough for me to switch to the cargo line (as opposed to the reinforced line I'm currently on), or will it not let me downgrade far enough?

Ye can downgrade to reinforced III. Then upgrade to Fortune Hunter IV. Ye will lose all the materials used to get to Copperhead, and will need all the materials to go to Fortune Hunter.

I penned a guide to Ship Customization that is stickied in the Sails and Ships section. Look there for more information.