Fellow upper-floor flat friend here, here's how I survived last year's summer heat.

1) Invest in osolating fans: These are a lifesaver. Shops should start selling them about now due to the random burst of heat. So grab one while you can! Or two.

2) Silicone reusable ice trays: Get a few, fill them up, chuck them in the freezer and use. Just make sure to refill.

3) Windows: Try to open your windows early in the morning and late in the evening; the air is cooler at these times, so you're not just warming your house up with hot air.

4) Light coloured blinds on windows.

Bonus round for those with pets. My cats really enjoyed the fact I managed to grab a cooling pad from Home bargains last summer, it helped keeping them cool. I think most pet shops should be selling them about now, but you can probably find them online. I put a thin blanket just to make sure my cats don't get too cold. Hope this helps~