Rabbits will usually do just fine if your home temperature is below 77 degrees, but if the room temperature rises above 77 degrees, turning on your air conditioning (if you have it) is recommended.
If you don't have air conditioning or you need to cool your rabbit down quickly, turn on a fan and let it blow on your rabbit. Setting a bowl of cold water with ice cubes in it in front of the fan.
A ceiling fan in your rabbit's room can help maintain comfortable room temperatures both with or without air conditioning.
If you don't have air conditioning and there's a breeze, open a couple of windows to help keep your rabbit cool while they plays with their toys.
Simply closing the curtains or blinds on the window will help block any sunlight from entering the room. This will help keep that room cooler.