Cannas are not winter hardy usually. So perhaps let it die down and shelter the dry roots over the winter. Then repot larger in spring, if the root survives the winter storage. I have never found them easy as dry root, either bought or stored. I have no experience of keeping them going over winter, or if that is possible.

As Dorjac says, the tubers are not easy to overwinter in their dry state as they can dry out and become hard or impossible to get back into growth next year. It is always better to leave them in the pot and store the pot in a frost free (but not warm) place. If the pot is fairly large there is probably enough residual moisture to keep the roots fleshy over winter. If it dries out too much, apply a VERY SMALL amount of water, as if you make them wet they will rot.
In the spring, turn the pot out and see how many good buds you have on the tubers. Usually you will find you can make another three or so plants from the previous year's tuber by carefully dividing them. Then you can start them into growth in their own pots in a warm place. I find it is better to just cover the tubers with compost and only fill up gradually as the shoot grows. I've rotted too many in the past by sticking the tuber in the bottom of a pot in cool conditions and giving them too much water too early.

Thanks Dorjac and Bertiefox. I thought I might bring my Canna into my conservitory for the winter, its not hot in there (only heated for the start of the day) but very bright and sunny (if we get any !) I'll just hope for the best I think, I'm no gardener as you've probably realised !!