By default all memberships renew unless you selected to not automatically renew either at checkout or by managing your subscription in the my account area. Automatic renewal is not applied to gift memberships by default.
If you are gifting a membership, then you will have to select "Automatically renew my gift when the subscription expires" at checkout.
If you are the recipient of the gift, then your automatic renewal status would have been set by the person gifting your the membership. You can set the gift to automatically renew by paying for a renewal and setting your membership to automatically renew.