Yes that is how it's done(you don't need to cancel explicitly though, there is an option of changing plans). You will recieve the applicable refund and will be migrated onto the new plan, on the final screen do confirm the amount of refund that you will get before moving forwared. For details see the following link
If you have any further questions or something is unclear during the process, get in touch with the support team they will help you out. To contact support, login to your account and navigate to the URL below. Make sure that the browser has cookies enabled, and all script blockers are disabled.
Type AGENT to avoid bots and talk to a human.
Also, be mindful of answering anyone who sends you a private message. See the following for more information about scammers