The eternal question: how to change miles to Kms on Forerunner 55

Just bought a Forerunner 55 and would like to record distance, pace etc as Kms not miles, on BOTH the app and the device. I can see where to edit the distance on an individual run, on the app, but even after saving it just reverts to miles. I have already changed the units to metric on the device so that's ok, but my summary stats on the app are in miles. Any advice appreciated.