The catheter is held in place by inflating a balloon on the end of the catheter inside the bladder. The balloon is usually about 10cc or the size of a walnut. If you know how to use a syringe, you may deflate the balloon by removing the water through the inflation port. If it is a new catheter you may just cut off the balloon inflation port with scissors as you were shown by the nurse, and it will deflate itself.