Repotting can cause unnecessary stress to plants and I would never advise repotting what appears to be a happy, healthy plant! I'm sure others will be along soon with advice and suggestions.
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!
That is one gorgeous Dumb Cane (Dieffenbachia seguine) 
