Its not difficult and well within the capabilities of a DIYer. But you need to work out where you are going to route the pipes - that's the hardest bit. If they emerge from a solid floor you may have to route them around the wallseither behind a cover or chased into the wall. You will need a couple of compression 10mm couplers to link the old/new pipes together. Then rebalance the radiator (its resistance to the passage of water will be higher due to the longer pipe lengths.