This video explains the procedure for performing a DIY (Do-it-yourself) change of the window regulator on an E90 BMW 3-series (2006-07 325i and 330i & 2008-2011 328i and 335i). The video was made for the rear, but the procedure for the front is very similar.

This is an easy way to save $300+, as the dealer usually charges over $400 to replace it but the part costs only $115 or so.