You can either remove the flowers as they fade and also remove the stem BUT leave the foliage and don't cut that away, allow the foliage to die down and this helps send much goodness and nutrients back down into the tuber, after the greenery has turned brown you can cut it away IF you want to have tidy borders, the dead foliage is quite tough so you may need snips to remove it.
After tidying up around the tubers I spread a handful of fish / blood / and bone meal as this is a nice natural slow release feed for all types of plants.
You can also leave the flower heads on the plant as the birds love feeding on them OR, you can let the seeds dry, (leave on the plant till you see the seeds about to pop out from the pods, then you plant the seeds in a pot of good quality compost, leave in a cool place till spring, you will get little green shoots like grass, the following year / spring, plant out in garden and mark the spot so you cont trample them or dig them up as you tidy, add label for future info or it's easy to forget colour, plant or flowering time.
Hope this helps you out.
Good luck and Best Regards.