It's very simple. Make hydration your priority more than ever. Wear bright colour loose clothes, dark colours absorb the heat. Hydrate properly. Run early, before the sun jumps above the horizon. Is that too early? Ok, then run as early as possible but DO NOT run in the sun and NEVER run when the heat is at its peak between 11am and 4 or 5pm. If you do (as I do), protect your head with an appropriate (surprise, surprise) bright coloured hat. Wear shades and put the sunscreen on. Hydrate like you've never hydrated before. Run slower than usual. Also, you will sweat lots. Why? Coz it's hot and your muscles when working generate even more heat. Btw, you're meant to be sweating, you are working out, remember? Finally, If none of that works, then don't run in the heat. Simple.
Running outdoors means various weather conditions. Hot/cold/wet/windy/sunny/nice/not so nice. If you make a choice and run outdoors, accept the weather for what it is. My father used to say 'if you want to do it, do it. If you don't want to do it and still do it, don't come back complaining'.
Enjoy the sunshine while it lasts, you'll get loads of vitamin D.