In order to remove the front strut bearings on your 1991 Cadillac DeVille you must first remove the strut assembly. With the strut off the car a spring compressor is used to remove the spring pressure from the bearing assembly. The bearing can then be removed and replaced. Compressing the springs can be a tricky and dangerous job, best left to qualified technicians. Please use the following link to find a repair shop near you - http://repairpal.com/directory?address=85501&car_brand_names=Cadillac.