By default, Eve will use units that are common in your region. In iOS Settings > Eve > Units you can switch Temperature from ° C to °F, and Pressure from hPa to mbar,mmHg or inHg from Meter to Feet in elevation or from Liters to Imperial gallons or US liquid gallons in Volume.
To change the temperature displayed on the front of Eve Degree from Celsius to Fahrenheit, navigate in Eve to Settings > Devices > Eve Degree.
You can change things to the units you would like to use in the Settings application that is built into iOS.
Select Eve, and then you will be given options to adjust Temperature, Pressure, Elevation and Volume.