The front sensors are just clipped on. Really easy to take off. Depress the edge of the cupeling (sp?) and just pull. Additionally, you can take a big wrench and muscle the sensor off. Once it moves a tiny bit, your good and slowly unscrew it. However, get a flash light and look really careful at the connector to the car and try to unclip it that way. It's really hard to unscrew the sensors with then still attached to the car; possible, but it's a pain.
Also, get yourself some anti seize grease. I forgot what it was called but at autozone it's in a small grey plastic can. It will help with future installs
2010 E93 M3 / MS Catless X-Pipe / AA Catback / Vorsteiner Vented Hood and Bootlid E93 Trunk / ADV1 7.1 Wheels GB / LS3 LED Lights / Harrop Supercharger