The best way is similar to dahlias or spring bulbs. Wait until they die back (but before a frost if possible) then dig them out, trim off the dead growth and store the rhizome in a cool place. If they are in pots then simply move them to somewhere cool (not cold) and when they die back trim off feed them and take them out into the open air next May. If you are prone to heavy frosts where you are then dig them up 'in the green' and move somewhere cool. Then just do your trimming.