WARNING: This page is about a different car, the 2010 BMW 135i, 2009 BMW 135i, and 2008 BMW 135i. However, it is still accessible from the selected car via links, so may be relevant.
Place cylinder head on special tool 11 9 000.
Press valve spring down on spring retainer with special tools 11 0 009 and 11 9 017.
Fig 1: Pressing Valve Spring Down On Spring Retainer Using Special Tools 11 0 009 And 11 9 017