More:Namco Museum Battle Collection: Galaga Arrangement

From GameWinners

Contents 1 Hints 1.1 Better upgrades 1.2 Ship select

Hints

Better upgrades

To get better upgrades let your ship get stolen, then let another steal your ship. Kill one, get the power-up, then kill the other bug. You will then get an ultra upgrade. Try using different bugs.
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Ship select

Complete the game (the last level is level 6-5) to unlock ship selection in Free Play mode. This allows you to select a ship upgrade before starting a level.