Changing a Facebook group setting from "secret" to "closed"

Question

How can I change the privacy setting of a Facebook group (500+ members) from secret to closed?

I can't see any option to do so in Edit Group Settings.

Answer 1

As of January 2016: It seems that at some point recently, the Facebook article quoted by AlvaroFG was edited ("about a month ago") and now reports that the cut-off number is 5,000. If you still are under 5,000 members you should be able to change.

https://www.facebook.com/help/286027304749263

Answer 2

You might if you are still under 5k members, as per Facebook rules after a group gets above a certain size (5000 users), you can only increase its privacy level.

Groups with 5,000 members or more:

• The privacy of the group can only be changed to a more restrictive setting (ex:Public to Closed, or Closed to Secret). We do this to protect members of these groups from having their posts shared with audiences they didn't intend.
• Once the privacy is changed to a more restrictive setting, all admins have 24 hours to change it back.

(Thanks Michael Bray)