How to Extend Part of an Image
Folks let me start off by saying I am an absolute beginner with Ilustrator, zero knowledge.
I have this stock .ai file:

Now I want it to be A4 size, so I opened an A4 size document and placed the image in it, so now it is like this:

How so I scale only the blue and red backgrounds so that they fill the top and the bottom of the page without scaling all the text and everything else with it?
Thank you and please kindly ELI5 if you do have time to respond.
