How to change from Fahrenheit to Celsius in Y!Mail bar?

I don't think you can change it permanently. However, if you click on the Weather, there is a little circular start like button. Click on that. There is then a C or an F at the top. If you click on it, it will change to C or F whichever way you want to change it.How to change from Fahrenheit to Celsius in Y!Mail bar?
Use your brain. Subtract 32 and then divide by 1.8. Thus 50 degrees F becomes (50-32)=18, 18/1.8=10, 10 degrees C.