How do I make my Media Gallery wider to fit new width

Hello,

This is the link to the page in question :

http://www.scrumptiousbunscakeschool.co.uk/classes/?preview=true&preview_id=29&preview_nonce=5018eaf466

As you can see, I’ve made the content width much wider than the original twentyfourteen template… I’m very new to this and have managed to edit stuff with the help of this codex… what I need to do now is make the gallery images the same width as the text/content… at the moment the gallery is still the width of the original template.

I have made a child theme, so would really appreciate any help in giving me the code to make the gallery the same width.

Many thanks in advance 🙂

Sx