I wouldn't open the window until it really cools down (5pm onwards) you don't want to let the hot air in. I'd also say if it's the room that faces the sun the most keep the door open. You can also try opening your loft hatch if you have one, heat rises so the hot air should naturally want to travel up there. I found it drops the temp by bout 1.5 degrees.
We've bought a humidifier- the Vicks one, it's a cool air one so although it's hot in the room it feels much cooler. This helped a bit with my Lgs room but we were the same for the past couple of nights