By pulling up some of the rhizomes and moving them to a new spot.

I use a sharp-shooter shovel and go straight down, then transplant like any other plant.

They are very hardy, even staying out of ground of weeks and still viable. in fact, just yesterday, I saw one of the small pieces that I had not taken care of from maybe 2 months ago. It was still growing its canna leaves just fine without any sign of wilt or unhealthy look.

So what I do, is find where I don't want it to grow any more, such as beyond a certain border, and stick my shovel straight down to that area. A little wiggle and the root comes out, and then it is given away.