Change image size in (gallery) attachment page

Hello, I’ve just installed twenty seventeen and it looks lovely except that the automatically created attachment pages (e.g. those you get when you create a gallery) only display a small image.

I was wondering if there’s an easy way to change this? I’m only a beginner, but comfortable with using FTP and hacking files, just can’t work out which ones to look at.

Would be grateful for any advice about changing the attachment page image size to something larger. Thank you.

• This topic was modified 6 years, 5 months ago by LAB18.