Is it possible, in photoshop, to make the dimensions larger once you've already created the document? I'm guessing you can since you can crop an image and make it smaller.

Go to Image > Image Size, and type in the new dimensions you want.
Of course this will distort it.

You can also do Canvas Size (right next to Image Size) if you only want to make the canvas bigger and not all of the layers bigger.

or you can go crop > select the whole document and then just make it bigger than it actually is

or go ctrl + alt + I to make erything grow