After you buy a pair of skates or boots the first thing you want to do is try them on to check for proper sizing. Try them on the carpet to keep them new in case you need to do a size exchange. Before I try a boot on I first make sure all packing in the toe area is pulled out. I then take the laces out of the top 3 or 4 eyelets of the boot.
I loosen the laces fully right down to the bottom of the boot. I then put the boot on. I taught the laces (barely tight) at the bottom of the boot (toe area), taught the laces in the middle of the boot (you don't want to crush your arch) then tighten the boot well at the top of the boot to get good ankle support. I then put the strap into the buckle and tighten it.
When tightening the buckle push the strap into the buckle with one hand while you pull the strap into the buckle with the lever on the buckle. You don't want to put 100% of the stress on just pulling the strap into the buckle with the buckle lever. 50% of the pressure should come from one hand pushing the strap into the buckle.
I then don't retighten the laces for the rest of the skating day, I only click the buckle 1 click at a time as the boot gets loose. Back to sizing. So once you have the boot on, stand up on the carpet for 5 to 10 minutes to determine if the boot is to big, to small or just right. If the toes hurt it's to small and it needs to go back for a size exchange.
Your going to have to determine if it's to loose or to floppy. Don't stand on them for 30 minutes or hours as speed skate boots are not meant to be worn in that manner. They are meant to work in a skating stroke with your heart beating at 150 beats per minute with endorphins flowing. Also don't walk on the boots, they are not meant to be walked on like shoes. At this point if the boots are to big or to small get them back in the box for a size exchange. If they're the right size the next step is Frame Alignment.