How do I remove my single storage plan to use a family pan

You don't have to remove anything. If you currently have a paid subscription, you can choose to use the Family Shared storage and it will automatically cancel your own, and refund you the unused portion of it.

Follow the steps in the link below to select the shared storage.

click here ➜ Share iCloud+ with your family - Switch to shared storage - Apple Support

When you switch to the Family storage plan your individual plan should automatically be cancelled. See the following from Share iCloud+ with your family - Apple Support

If a family member is already paying for their own iCloud+ plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.