Here are two good DIY's... (on the e90post)...
DIY – Water Pump & Thermostadt Replacement (2007, 335i w/Automatic Transmision)
http://www.e90post.com/forums/showthread.php?t=784416
Pictures: Electric water pump + thermostat replace
http://www.e90post.com/forums/showthread.php?t=347412