Cut the flower stalks of when they've finished flowering but don't remove the leaves - the plant still needs them.

thank you. even if the foliage is all brown still leave it on?

At Hyde Hall the RHS garden the leaves were cut off later on in the season than just now, past the flowering time. If the leaves are brown, they are no use to the plant. So, if you want to tidy up feel free, surely. As an insurance you could try taking a piece of the bulbous root from the side of the clump and growing it on. In case the clump is failing. My Daylillies are revelling in it this year in all the rain.

Yes, brown leaves are no longer doing anything - its the green ones you need to leave on.