A simple solution to this would be to use scale to size your GUI, but can often result in stretched elements that look ugly. You can counteract this to a certain degree with 9-slicing.
If you want to maintain the exact aspect ratio of your GUI, I recommend using scale for the root (greatest ancestor) GUI, along with an UIAspectRatioConstraint. This will maintain your GUI’s aspect ratio (and therefor aesthetic) while scaling with any screen size. It’s what I personally use for my GUI.
Good luck! 