There are several places where you can create custom messaging for your memberships. The Custom Messages tab allows you to craft your membership page explanation and an area for a membership cancellation message. It's important to think through both of these in how you want to communicate clearly what's offered and the steps to take. You may also consider including a survey in the membership cancellation message to learn why some of your subscribers may be leaving.
Below you can see an example for where this would show up on for general users as they are looking at joining your community.