It is a lot easier on the Centerstand, because you can rotate the wheels to get the air valve positioned properly for best access. To turn the front wheel, I just push up a bit on the front fairing underneath the headlights. You don't have to get the front tire off the ground - just unload enough weight so that you can turn the wheel with your other hand.
If you use the sidestand, you'll have to roll the scooter to position the air valves.
As Randy said, you should do this before riding the scooter. Riding heats up the tires and causes air pressure to increase. The recommended settings are given for cold tires. If you do need to check tire pressure after riding, let the scooter sit for at least 3 hours before doing so.
An electric air pump is a great investment, since you can use it at home to adjust tire pressure before riding. I wouldn't be without one. If you absolutely HAVE to go to a gas station to fill your tires, try to use one that is within several miles of home.