Hi Teery! Thank you for your question. Its sweet and simple. You can cut them them all the way down. I usually just cut back the spent blooms first, and keep the greenery  for awhile.  Then once the greenery starts to turn, and then I chop them all that way down. It wont hurt them at all. Then next year they will come back.  It's always scary cutting everything off at first,  but then you will be happily surprised next year. Good luck, and you have this.

Elizabeth-MGV