1. Go to the Start screen and click the Weather app tile.
Go to the All apps screen and launch it from there.
2. Open the Charms bar and click Settings. Charms bar can be accessed by moving your mouse to the bottom right of the screen and then move it up, or pressing the Winkey + C on your keyboard.
3.Choose Settings from the right side bar. You can find it right at the top of the bar, under the Weather text.
4.In the Settings section, find the Units option. This option allows you to switch between Fahrenheitand Celsius unit. The small dot indicates which unit is currently used.
I hope this solves what you were looking for.Else I'm here to help you further if needed. :)
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