If there is a problem
These are your statutory consumer rights. If any of them are breached you are within your rights to go back to the seller, who will then be legally required to remedy the situation in a number of different ways, depending on your situation and the nature of the complaint. The law requires you to act reasonably too, so if the problem is minor and can be repaired easily, within reasonable time, at no additional cost to you and without causing any significant inconvenience, then the dealer can insist on a repair as a first option. But remember that this will not stop you from taking it back if the repair is unsatisfactory or there is something else wrong with the car.
If the car cannot be repaired, if the repair is unsatisfactory, or takes an unreasonable length of time, your next option would be to have it replaced. If this is undesirable or impossible, then you can request a refund, although if some time has passed, you should be aware that any the refund given may well take account of any use you have had of the car since you took possession of it.
In situations where you would like to keep the car and undertake to carry out the repairs yourself, you have another option, which is to request a discount on the price paid.
