Resizing all text (of different sizes) within a text box at once

Hi all! Years ago, I used Quark. I haven't used it in a long time, so I don't remember the exact key command... but I want to know if I can do something in InDesign that I used to be able to do in Quark. Imagine having a text box... and in it is a 12 point headline and 9 point text below that headline. I want to enlarge the whole thing... maybe bring the headline up to 18 points and the text up to 15 points (or whatever would be proportional). Is there a way to do this in InDesign? I've never been able to find it. And I find myself wanting to do this periodically. I'm not looking to enlarge the text box itself... just the text within it. Thanks.