How to Upgrade your Ships?
1. Go to Fleet Factory and select a Ship (Frigate, Cruiser, Destroyer, Battleship)
2. Tap Ship Upgrade
- Upgradable Ship will show an active button 
- Non-upgradable Ship will show an inactive button 
3. This will show the cost of the Upgrade. Set the number of ships you want to upgrade.
You can also scroll up and down to show the complete list of resources you need to upgrade.
4. To confirm, tap the Ship Upgrade button