Cut them back.

I don't cut mine back. I hand pull dead stems out or use a small rake.

I cut mine back about 3-4 weeks ago when it was nice weather. We have had nothing but frosts,cold weather and no rain since then and my blue fescues have grown completely back and look great. Other ornamental grasses I cut back have done nothing since then and my lawn which I haven't cut yet looks terrible but the blue fescues are amazing. I am waiting to see how big they get if they keep growing the way they have so far this spring!
Debbie

Evergreen ornamental grasses do not require pruning or cutting back in late winter or early spring unless their appearance demands it. And that can vary widely depending on location. In my climate (and that of BOS888), evergreen ornamental grasses - like both the fescue and oat grass - look pretty uniform in appearance year round. And that's pretty neat and tidy :-) Just raking out any dead blades is sufficient. I am more inclined to cut them back (actually, trim lightly) when they start setting seedheads - those I find messy.

Some evergreen grasses or grass-like plants can actually be harmed or their growth stunted or compromised if cut back hard. Best to do some research first.

In the past I haven't bothered to cut back my Blue Oat Grass but like others have suggested, I simply pulled out the dead stems. However, I cut one back and within only a week it has beautiful bright new growth. The difference between the two techniques is amazing. The new growth is just so incredibly bright and beautiful.

I know different people in different areas have different experiences with the same plants in their different gardens and different soils, etc but I'm definitely going to cut back all the other Blue Oat Grass in my gardens.

One must learn by trial and error and do what works best for you :) the beauty of these forums is sharing what works in different parts of the country and world :)

I do mine the same way Steve does, but I do it twice a year. Once in the late winter and once as the flower stalks start to turn brown (meaning the seeds are ripe). I cut them back about two thirds, into a round-shaped hedgehog-looking mound. The only exceptions are a couple each of my favorites, which I allow to self-sow and/or I collect their seeds. They all grow back beautifully.