Whenever any portion of the cost of a parking lot which is to be discontinued has been paid for by special assessment, the useful life of the parking lot shall be determined by the governing    body. If the period of time determined to be the useful life of the parking lot has not completely elapsed, the governing body of the municipality shall direct the cancellation of uncollected installments of special assessments previously levied for the same improvement, and the refund of installments paid, plus interest calculated at four and one-half percent per annum on the refunded prepaid installments, from the general fund of the municipality to the extent determined by it to be necessary to make the original assessments and the subsequent assessments bear as nearly as possible the same relation to the total benefits derived from the improvement by the respective properties assessed.