Resize background?

Hi, all, Toonicorn here, back for some more of your helpful and sage advice, if I may.

I'm creating a new comic, and so I opened a new file page - a blank white one, letter-sized, as the comic's background. After putting all of my renderings on it (on layers - each drawing is on a separate layer), I'd like to enlarge the letter-sized background because I've discovered that it isn't big enough. But I can't figure out how to do that. I just need to make it a bit longer. Is there a way? And thanks in advance! :)

utilities / options /page size tab - you can define the 'paper size' there

I think you can also drag it with the mouse/pen by default but I have that disabled because I kept doing it by accident

Thanks, Handrawn - it worked! :)