In order to do ship upgrades in Galactic Civilizations II, a few conditions must be met:
- You must have a different custom ship type of the same size category
- You must have a positive credit balance
In order to actually upgrade a ship, you must remove it from orbit of a planet or a fleet, and then select upgrade from the ship pane of the interface.
In the popup window it will show your current ship stats in the top section, and all of the other ship types of the same size category in the lower pane. Selecting another ship type will show a summary in the lower pane with changes to ship statistics as well as the cost to upgrade a single ship. In order to complete the upgrade click on 'Upgrade'. Upgrades may take several turns.
If you wish to upgrade all ships from one type to another, immediately below the picture of your base ship is a checkbox for "Upgrade All". Checking this box will upgrade all ships (including those in orbit or in fleets). The price figure in the bottom pane also updates to indicate the new price.
"Upgrading" can also be used to revert a ship of the same size to a less powerful—but cheaper to maintain—version of itself. Possible application of this is to make two versions of a defense ship, one with engines and one without. When the ship arrives to its destination "Upgrade" the ship to the version without additional engines in order to lower your maintenance costs.
The AI will redesign ships once every six months unless the "Intensive Algorithms" is checked. Under Intensive Algorithms, the AI will redesign once every 10 weeks. It will upgrade existing ships provided it has the need and money to do so.