It depends entirely on how you abtained the finance; the two most common for the purchase of a vehicle are hire purchase or a personal loan.
Hire purchase agreements are regulated up to quite a high amount under the consumer credit act. The goods remain the property of the hirer not the client until the end of the agreement and the vehicle should not be sold without the agreement of the hirer. If you have not missed any payments and have paid at least half the amount of the total purchase price as stated on the agreement you may return the vehicle to the hirer and have nothing further to pay, give written notice to the hirer who may put obstacles in your way and challenge your right to end the agreement, this is not correct and your right to end the agreement is unconditional. If you default on payments and have not reached a third of the total amount the hirer can repossess the vehicle without a court order, over one third the hirer must obtain your permission or go to court.
A personal loan at a fixed or variable rate of interest is again regulated up to a high level by the consumer credit act and are usually over a set number of years. If you have a personal loan and have other debts seek specialist advice.