Hi there! First post here! I'm a new brazilian player!

I need some help folks!

I know that a enemy power token is put right above the original house power token if a enemy unit leaves a invaded capital. But what happens when the enemy unit stands there? What happens with the original power token?

Regards!

Nothing happens to it - it's printed on the board.

Power tokens are only placed when vacating an area, in order to maintain control. If there are units in the area, they have control - no need to place a token.