If your home has a second story, nobody has to prove to you that heat rises; you already know that. For many, the answer is to crank up the air conditioning even more, but that typically just turns your living room into an ice box. The real key to upstairs comfort is limiting heat gain and circulating the air.
Ceiling fans make upstairs rooms feel cooler by circulating the air and providing a cooling sensation on your skin. Just be sure to turn them off when you leave to avoid wasting energy.
Invest in thermal blocking drapes and close them whenever there is direct sunlight. This will limit heat gain, keeping your entire house cooler.
Because we're so used to air conditioning, it's easy to forget that sometimes it's actually cooler outside. On cool nights, open your windows and let that air in. If it's still too warm upstairs, hire a qualified professional to check your attic for air leaks and ensure that it's properly insulated.
Now, go ahead and enjoy your upstairs this summer. It's cool.