Garageband will not update

I'm on iMac i3 v 10.6.8

Garageband v 6.0.4

I turn on, it says there's newer Garagebandversion.

I search for update, says none found.

I manually download v 6.0.5

I open .pkg, it says must be opened by Garageband 6.0 or later.

I'm trying to update this because my iPhone files won't play unless I have 6.0.5.

What gives?