AFT software supports ISO and English units and provides a variety of ways to select the units to be used. For example, in the Output window you can change units 'on the fly' for a specific parameter by double clicking an output column header and selecting the desired unit from the Change Units window.
To globally change the unit system, go to the Options menu and select Parameter and Units Preferences. Select the Unit Preferences tab, choose the Default Unit System then click the Apply Default Units button. This will both apply the default units for the selected unit system and change the preferred units.