My [Alpine] Ski boots are too big, how to make them smaller?

A 28.5 boot is the same as a US mens 10.5. If you wear a 12, then the 28.5 should be way to small, not to big. There are a couple things you can do. As far as the buckles go, the piece on the boot can be unscrewed and moved over in order to make the buckle tighter. You can also try wearing thicker socks, just make sure the socks are made for skiing. Beyond that, there isn't much you can do that is cost efficient. You can go to a boot fitter, but that can cost you $250 or more. At that point you would probably be better off just buying boots that fit better.

Go to a boot fitter and see what they can do for you, and if they can fix those buckles. You're saying too big in the title, and too small in the text. Just because your toes wiggle does not mean the boot is too big. My toes can wiggle in my boots, you need some room for blood flow and circulation, and the toes should not be smushed. But your heel should be secure in the boot and the foot should not slide around in your boot. Liners surely can compress and/or age over time and affect the fit. If you are a racer the fit of your boots is the most important factor, a boot that doesn't fit right is $500 wasted. Or just wear thick ski socks.

You need new boots. It can be dangerous and painful if your boots don't fit right.