For the period between 6 months and 6 years after purchase, the retailer is obliged to remedy any fault which arises out of an 'inherent fault'. This refers to something which was wrong at the time of purchase (even though it wasn't evident at the time) such as poor quality components or poor workmanship.
Unlike the first 6 months after purchase, there is no automatic assumption that the problem is due to an inherent fault. It is for the purchaser to show, based on the balance of probabilities, that the most likely cause was such a fault. (If it seems more likely that the problem was not the result of an inherent fault, the retailer is not obliged to remedy it).
If it can be established that the problem was most likely to have been caused by an inherent fault, the retailer must either repair or replace the product. However, the retailer has the right to decide which remedy to apply. i.e. you have no right to demand a replacement product if the retailer prefers to provide a repair.
Chris