You won't kill the irises. It's time to dig them up and divide them anyway- tall bearded irises should be dug and divided every few years for maximum bloom.

You can also plant them in the middle of summer. Just don't water them too much if it gets very hot.

Check out the FAQ at the top of the iris forum for directions on how to divide.

Here is a link that might be useful: FAQ

If you like books and pictures, there is a good page in "Growing Perennials in Cold Climates" by Heger and Whitman page 397 that shows pictures of rejuvenating an overgrown iris bed. I don't know if you are in a cold climate, but if so, this book could be available in your library. But FAQ link gives more detailed instructions about what to do with the irises after they are extricated. Good luck!