Go to File -> Board Setup
On the left, under Layers, select Text & Graphics.
Fill the table with the values you got from your board house.
Then go to Edit -> Edit Text & Graphic Properties
Under "scope" check what you want to change, e.g. references.
Under "filters" you can further limit to e.g. top silk screen.
Under "action" you specify the new values. Here, select the bottom checkbox "Set to layer default values:".
Press OK