If you would like to extend the end date of a membership, head to the client profile that has the membership you would like to extend. Select the three dots next to the membership > Edit. From here you can then select a new end date, once done select 'Save changes'. The end date will now have been updated.
You will not be able to extend a membership if the membership has expired. Once a membership has expired nothing can be done and if a member wants to continue their membership they will have to sign up to a new membership.