Not everyone has high powered devices to game on so I was looking for a way to allow people who play my game to change the resolution. The forum member Aphrodite told me how to easily do that. All you have to do is combine the actions "set canvas size" and "set layout scale" like this:
My original resolution was 1600x900 pixels. To find the correct setting for the scale action, I just divide the resolution I want to change it to by 1600, getting the correct ratio.
This can be combined with an options page and touch or mouse objects to allow the user to change the resolution.
I hope this will be helpful and thanks for reading!