The phrase "to roll down the window" means to lower a window by pulling on a handle or using an electric switch, in order to let air or freshness into a room, vehicle, building etc. Full definition
However, keeping passengers comfortable in hot weather by rolling down the windows or using the air conditioning (AC) can reduce fuel economy. (fueleconomy.gov)
What ever happened to just rolling down the windows? (cnet.com)
Keep the windows up, and if you have a window lock, turn it on, so your pet doesn't accidentally roll down the window. (tampavet.com)