You can treat this as you may for most succulents and that is, repot them when they become aesthetically too large for their pot. There is no 'rocket science' needed. However it is usually best never to put plants into an overly large pot - anyway that too is also easthetically bad.. In other words as long as your plant looks 'right' in relationship to it's pot then all should be well culturally. Incidentally the generic name should start with a capital.

thanks for the info.

Dioscoreas generally start growing new roots before they form a top shoot and its a good idea to have them potted up before that happens eg. in December-January. Keep the caudex shaded and the vine growing in dappled light. They respond well to a mix with rotted compost in it along with a dose of osmocote and I also use some Dynamic Lifter! Keep moist at all times, even when dormant,when young especially. The roots die off if left dry out and they find it difficult to get started again. If you accidently break the vine off, it won't regrow that season. Hope this is of some help. Joylene.