What exactly is the dilemma? Do you have a medical condition that impedes carrying a bike up and down the stairs, or is the stair well too narrow, or something else? Generally that should not pose much problems. Of course, a lighter bike makes it a bit easier, but one gets used to it either way. Just take it slow and take care to not bang against the walls and/or handrail. The grip used varies with the frame shape and size, but you should be able to figure out easily what is the most comfortable way for you.