I use a modified version of a "Cyclocross Carry" to get my bikes to my third-floor walk-up.

This video demonstrates several versions of the Cyclocross Carry. The method I use is from around 1:35 to 2:00 in the vid.

Yes, it takes a little practice so you're not banging the wheels into the walls, but as you see, it's done one-handed and I use the other hand on the stair rail.

True, in the vid he's using a svelte racing bike, but the method works well even with my commuter with full fenders, racks, lights, battery packs, and a modest load in the panniers.

If your bike has no fenders, going downstairs is even easier. Use the "LBS Rear Wheel Roll". Squeeze the rear brake and pull the bars up and back so the bike's standing straight up on its rear wheel. Release the brake and roll it along. Going down stairs, control how fast it moves with the brake. You'll find to can stop it and balance it right on the edge of a step.