The term of office of a parish councillor comes to an end after four years, the next time for you being May 2023. Period. Councillors do not have to 'stand down' as their term of ends, and elections will be called by your principal authority. Election rules apply - simply, if there are more candidates than seats there will be a contested election, if the number of candidates equals the number of seats they will be elected unopposed, if there are less candidates that seats you will run with vacancies until those are advertised according to the rules.