You would need to either extend the X or Y axis. I think it structurally would be a lot easier to extend the Y axis as it is just sitting on the ground, while a longer X axis would mean more weight on the arm and more torque on the Z carriage and Z axis, probably causing it to bend a little bit during printing.
For a longer Y axis, you would need to extend the frame in that direction by 100mm. The current bits are 350mm, so you would need 450mm. That consists of the two 12mm steel rods, and the aluminium extrusion. Then you would also need to get a longer Y belt, as well as a longer cable for the hotend (does not necessarily have to be a ribbon cable though).
You would also need to modify the Y carriage to fit the larger bed. It might be enough to just put something like a piece of plywood on top of the existing carriage and then the heater on top of that, but if that is not enough support, you would pretty much have to design your own new carriage. Shouldn't be too difficult, just take some existing design (the wooden stock one, or the one someone here posted that was printed) and extend it a bit.
For extending the X axis, you would need some other frame parts extended. The same 450mm 12mm rod (but just one), and also longer X-rib and X-plate. And same thing there, longer belt and extended cables for the hotend. Even then, you would have to redesign the Y carriage somehow for the larger bed, and just having 100mm extra bed hanging out outside the frame might not be a good idea as supporting it would be quite difficult. For that, you would probably need to widen the Y axis a bit (move the two 12mm rods apart a bit, and make the bed supports longer. It is possible it can be done with adding some stiff suports along the Y carriage (like square carbon fiber tubes) without adding too much weight.
