You need a much bigger pot that will retain much more moisture so your plants will get through the hot days. A bigger pot will also give your tomatoes more room to grow. Try to get a ~5 gallon pot. Be sure it has holes in the bottom.
Wait to transplant until things cool off a little or at least move the plant to a cooler spot and transplant in the evening. Pick off the withered fruit (and any damaged leaves) before transplanting.
Good luck!
