Each year, you have a chance to make changes to your Medicare Advantage (Part C) or Medicare prescription drug coverage for the following year. This annual enrollment period is called Open Enrollment and takes place from October 15 through December 7. The changes that you make during this enrollment period will take effect on January 1, 2014. If you decide to stay with your current plan there you don’t need to do anything. If you want to make changes, here's what you'll need to know.