in spring you should see that there are areas that look like 'creases' between the leaves. the plant can be pulled apart here into smaller sections.
i have been brutal in the past and just cut through the plant again in spring with a knife/garden spade. planted the pieces up and let them grow.
hope this helps.

This year, as Sunburngirl says , in the Spring I checked around the base of my plants and found stems with roots already growing. I pulled these off and grew them on without loss.

how did you know I burn easily :o)) cutsand......

Whoops, raincoat and dark glasses. Sorry Seaburngirl.