How can I change the temperature unit in Lollipop's lock screen?

Today, Lollipop became available for my Samsung S4 and I upgraded. Since then, the lock screen shows the current temperature: As you can see, it shows "61 °F". Since I am located in Continental Europe, I prefer Celsius. How can I fix that? As you can see in the others screenshots (lock screen configuration), "Additional Information" is "On" and greyed out, and accessing the "lock screen widgets" menu item only lets me configure the personal message, nothing else. I do use a third-party weather app ([Weather & Clock Widget](https://play.google.com/store/apps/details?id=com.devexpert.weather&hl=en)) , but I don't think this is related, since (a) the third-party app does not contain a *lock screen* widget and (b) the app is set to Celsius. I've found [someone on the Internet with the same problem](http://www.androidpit.com/forum/645867/samsung-galaxy-s4-lollipop-lock-screen-temperature-unit-problem) , but I haven't found a solution yet.