Water thoroughly prior to removal from the old container. If possible, cut the old container away from the root mass gently. Avoid lifting the entire plant by the trunk. Score the bottom of the root mass in a "X" pattern with a sharp knife about 1" deep into the roots and carefully spread each "quarter" away from the others. Make a small mound or hill in the new container with the new soil media and place it on top so that the top of the root mass is at the same level as before (slightly elevated is ok as well). Once you have covered all roots with the new media, water again to insure their are no air pockets and to help the new soil to settle. These steps will minimize stress when moving up to a bigger container. This of course works for all plant material, not just Cannabis.