Some effects Downgrade Invaders, representing gradual population loss. To Downgrade an Invader, Replace it with the next smallest Invader piece:

To Downgrade a City, Replace it with a Town.

To Downgrade a Town, Replace it with an Explorer

To Downgrade an Explorer, Remove it.

Downgrade is a special form of Replace, so it follows all of the Replace rules (doesn’t generate Fear, preserves Damage taken, etc.)