Look at your code:
pst4 = con.prepareStatement("UPDATE CarRegistration SET AVAILABLE='No' WHERE
CAR_NO ");
pst4.setString(1,car_id);
The SQL contains no parameters (or even a valid SQL WHERE clause) - which is why index 1 doesn't exist. Perhaps you meant this:
pst4 = con.prepareStatement("UPDATE CarRegistration SET AVAILABLE='No' WHERE
CAR_NO = ?");
pst4.setString(1,car_id);