Press and hold the F4 key down to get into the configuration menu (Dip Switch 1, located under the small back cover on the rear of the indicator, has to be on).

Under the scale menu, scroll down using the F3 button until you find the menu "Allow kg/lb Edit" change this setting from Disable to Enable.  Press the * key to save and then zero key to exit. Now when you go into the normal weight display the F3 key will have the lb/kg symbol next to it and the key will change between units.