leave them, they give the bulbs nourishment for next year, they will look unsightly for a little while.

Also, give them some liquid feed to help them build up nutrients for next year.

Dead head though so they don't set seed.

yes dead head first then give them a feed to help build up the bulb for next year. 6 weeks is the usual time to leave the foliage but if they have died back before then, then just pull the dead leaves off