Before that the temperature unit is based on the country of the weather and cannot be changed.
So if you purchased the frame after nov. 1st 2014, first make sure you downloaded the latest software version.
Then go to "Change Settings" menu and then to "date & time" inside you have a choice between Celsius and Fahrenheit for the weather.
Just click on it and select what you prefer.
Have a nice Pix-Star.