This is how we did it.
1. Boat out of the water.- we do not have a road trailer only a yard trolley. Our boat sits with about 63 cm clearance below to the ground.
2. Lie under the boat and look at the forward end of the centreboard.
3. Locate the 12mm Allen key head bolt and remove with Allen key tool. We used a ratchet driver.
4. In our case, with the boat sitting low to the ground, it is not possible to drop the centreboard enough to disengage the plate from the fixed pivot pin.
5. We had to dig a hole in the ground to give us a total of 77 cm clearance below the boat.
6. This is not enough clearance to fully remove the plate from below the boat.
7. So.. we removed the table from the top of the centreboard case, this is quite simple but there are a lot of screws and a drill driver tool helps.
8. Now that the plate is disengaged from the pivot pin, it is possible to lift it using the control lines upwards into the cabin space, enough to access the knots where the lines attach.
9. Join the new lines to the tails of the old ones and pull them through. In our case we couldn't undo some stopper knots so we had to cut our old rope.
10. Complete the job by carefully relocating the board onto the fixed pivot pin - you can feel when it in place. Refit the Allen bolt and the table.