You have to stop expressing your milk gradually, otherwise you will be in pain suffering from engorgement and leakage. I stopped expressing within 3 days and suffered serious engorgement and was very painful whenever I carried my baby.
I think you should do it gradually over 2 weeks, e.g. increase the interval of expressing gradually, reduce the number of pumps gradually. The body will take the signal no need to express so much milk and will gradually stop producing milk.
Remember, dont't stop immediately, it will be a very painful process.