Hitting the Promote icon (blue up arrow) 
on the Milestone Plan Page selecting a Milestone promotes it up to the next level in the WBS hierarchy (so, for example, promoting a Milestone from the Project level will result in it appearing in both the Project and Programme levels; promoting it again, from either the Project or Programme level, would result in it appearing also at the BCP level).
Note that when a Milestone is promoted it is flagged as promoted wherever it appears in the hierarchy (i.e. at the level from which it has been promoted as well as the higher levels). Thus if you see a Milestone flagged as 'promoted' you know that either it has been promoted from this level or to this level; you can tell which by examining the Promotion Pyramid.
Note: A Promoted Milestone can only be amended in the Plan in which it was originally created.