Hire an attic insulation professional to install a radiant barrier spray. Radiant barrier spray, according to A Cooler House, prevents sunlight and heat from entering your attic. The top coating of the spray acts like "aluminum foil" that "reflects" incoming light and heat back out of the attic.
Open the attic window if you have one. Install a window fan in your window. Adjust the fan, if you live in a cool weather state -- such as Washington or Vermont, for example -- so cool air is blowing into the attic. Adjust the fan, if you live in a hot weather state -- Texas, for example -- to pull hot air out of the attic.
Install ceiling fans in upstairs bedrooms. Keep bedroom doors open during the day and night. Open the windows to help circulate air in cool weather. Open windows and working ceiling fans will consistently move fresh, cool air throughout the second floor.
Install two energy-saving 5,000 BTU window air conditioners at opposite ends of the second floor if you don't have a central-air system. Close all windows before operating the air conditioners. Operate the appliances simultaneously to flush cool air toward the center of the second floor. Keep ceiling fans on to help air circulation. Adjust air conditioners to function automatically, if possible, to turn on and off when the upstairs temperature drops below a certain level.
Contact a professional HVAC specialist if you have a central-air system to inquire about installing alternative temperature thermostats for the upstairs and downstairs.
Avoid cooking on the stove or using lower level fire places at night to prevent the rise of heat before bedtime.