Can I change the wheel speed sensor, front wheel?

As far as I know, the front wheel speed sensor is part of the hub assembly. Talk with your local parts store to confirm this.

there should be one small bolt holging it in place. why are you changing it,is there a code for that sensor?

The decision to replace the Front Wheel Speed Sensor assumes you have verified the sensor is the problem. A continuity check with a good-quality multi-meter should indicate a DC resistance of 900-1300 Ohms. If this is ok, check continuity between the sensor mating connector (two contacts) and the EBTCM (Electronic Brake and Traction Control Module) connector, pins 22 and 24 (separate inputs). The Cadillac Shop Manual describes the front wheel speed sensor as 'integral' with the wheel bearing. The sensor (a ring and pig-tailed sensor) should not be reinstalled, but a new one should be installed. After removing the hub and bearing assy, a 'Sling Ring' is removed from the Speed Sensor housing assy, using care and a suitable size screwdriver. This exposes the 'speed sensor', itself. Pry out the existing one and install a new one using an arbor press. Reinstall the wheel bearing with the new sensor installed. The most difficult part of this job for me was the extraction of the wheel bearing assy from the splined half-axle shaft. I used a heavy duty 3-pronged 'wheel puller' I purchased at Harbor Freight. The loaners at the local parts stores in my area all use the same brand 'pullers' and their cast configuration did not allow use of the vehicle's lug nuts-what's a guy to do!!! If you can gain access to the Shop Manual, see pages 5E2-116,117 and 5E2-46.