Step 1: Find out the specs for the wheel you want to buy and not just diameter and bolt pattern, you need to know width, backspace, AND hub bore. Hub bore and bolt size are the two most vital specs, if they don't match nothing else matters. If the hub bore of the new wheel is smaller than the hub of the car it's going on there's no way to make it fit without machining out the hub. If the donor hub is bigger then the car it's going on then you just need to source hub rings to fill in the gap.
2013 GTI Wheel
57.1mm hub, backspace from 49 to 54 (but actually shows one of the options is a 16x6.5 wheel with a 50 backspace, important for below)
2007 Golf Wheel
57.1mm hub, backspace between 47 and 54 depending on width but look at that, there's that same 16x6.5 with a 50 backspace. Score LOL
On the back of the wheel there should be stamped the width and backspace to confirm but all the OEM sizes are pretty similar to those on the GTI so shouldn't be a problem.
Step2: If there were vastly different you would want to plug the specs into that willtheyfit site I posted and it will show you a visual representation as well on where the wheel and tire will sit compared to panel edge and suspension.
Step 3: Profit