Best to leave it until it is 5 years old although if you are in a rush 4 will do or even 3. But you will wait longer for it to start cropping again. Dig it up in either early spring, before it starts to fruit or late autumn, after it has died back. Just chop it into pieces but again best if you just make sure that a growing node is on each piece. No point in my describing these, they are obvious. Replant ASAP in the areas where you want the new plants. If you want to force it then wait at least 3 years before doing so to give it time to 'settle'.