Prerequisites
A: User must be logged in.
B: User must be granted at least "power user" role. Check this with your administrator.

By making a release official, all packages contained within a release will have their dependencies locked to prevent any further alterations. Also, users will be disabled on adding a packages, removing a packages, and moving to a different Base view.

1. Select a Release by selecting
Project Name > Version Tree
See how

2. Select from drop-down menu (located on the top-right corner)
Release > Make Official

Release will be Official Released.

See also
New (unofficial) Release, View History of Release