The old leaves on evergreen ferns (and other evergreen perennials) often look beat-up by late winter, even if not smothered by a snow pile. It's normal and you can trim off any you wish to remove, although there may be some benefit to leaving them a few weeks longer as a mulch of sorts that can insulate any newly-emerging fronds as we move into a period of warm spells interspersed with overnight frosts. New growth will emerge without difficulty and will cover-up the old foliage regardless, but if you want a cleaner look, you can trim off the all-brown or bad-looking fronds in the coming weeks and compost them. Bent or kinked fronds don't always die off right away, so you can focus on the brown fronds and leave the green ones for now, since they may still serve to feed the plant until they actually turn brown.

Miri