Want to switch providers? The new provider will handle the number transfer. You'll receive a final invoice for your subscription. Do you have a prepaid SIM card? Keep in mind you can't transfer your credit or bundles, only your number.
Want to cancel your number? If you have a subscription, you can do so in your SIM card settings. If you have a prepaid SIM, you can simply stop topping it up or send an e-mail to email@example.com using your registered e-mail address.