You should probably be alright, as long as the water is well oxigenated and clean (that is, no
NH3,
NO2-, controled
NO3-). When my fish (also tiger barbs) got ich, I "cooked" them at 93F for 3 days and then 86 for another 7 without any fish loss. The ich is gone and the fish are normal again.
In the future, you may want to make sure that you didn't leave your fish tank near a window or direct sunlight, as that raise the temp relativelly fast on a small tank. The method advised should work best, it is sure the easiest since it will bring the temp somewhat uniformelly and require the least work, but there is another thing you could do, depending on how fast you want to bring the temp down or if you don't want to buy a fan.
1. Move your fish from the tank (i.e. put them in a bucket with the water from the aquarium)
2. Add some cooler water to the tank (not too much) until you reach the temp you want (for tiger barbs 78-83)
3. Aclimitize fish back (that is... SLOWLY and in small quantities at a time - add the new water from the tank to the bucket where your fish are. For instance, if you have about 12 cups of "hot water" with the fish, 1/8 cup every 1/2 hour until the temp in the bucket is the same as the tank).
4. Fish back in the tank...
If you have the fish at work, I would just go with the fan idea
its less work and effort, just thought I post it anyway