The best way is to create a small slit on the inside of the jeans, cut the waist band in half pull it out through the hole and then sow the hole on the inside back up DO NOT MAKE THE CUT ON THE OUTSIDE
The easiest way would be to just cut it off, but then you lose the seam allowance. The other option is to pull the stitches out by hand with a seam ripper, which will take a long time.
The best way to remove a waistband from your jeans would be to buy nice fabric scissors from either a craft store or from the fabric section of Wal-Mart. These are made for cutting fabric and should cut jeans.
Using a seam ripper I would start at the front of the waistband and take out all the stitches holding it on and after your done it should be ready to just take off.
