Follow your doctor's recommendations for what you should do prior to surgery re: food and drink. I can't promise you no discomfort, but you will be given a local anesthetic.
There is little that one can do to prepare for kidney stent removal. It is a fairly easy procedure. The physician can use a sedative and a cystoscope and go in and remove the stent. Sometimes the stent when placed will have a tail that can be pulled out.
