I am new to the MoO series of games (not that it should be relevant, but anyway) I am sick of having to give my viceroys a slap upside the head and redo their build queues because they refuse to build the new ships I have taken the time to research and design... and I cant seem to get rid of any ship designs once they are created.
Mark any design that you are sick of with the MARK OBSOLETE button. If the hide obsolete is check, they will not show up in the list of items to build. Now when the Vicory want to build a ship it will choose one of your new designs.
If you want to get rid of the ship and it is built, then you must scrap it.