d-PIT have produced a quick upgrade guide for the BlackBerry Enterprise Server v4.1.6.

In order to upgrade to version 4.1.6, you must currently be running any version within the v4.1 stream.

This guide outlines how to upgrade a BlackBerry Enterprise Server from version 4.1.x to v4.1 SP6, and is available free of charge from here.

 Download: BlackBerry Enterprise Server v4.1 Service Pack 6 for Lotus Domino Upgrade Guide