Like any other evergreen plant, older foliage will die off from time to time and need to be removed. I grow a number of different varieties of flax myself and find they need routine grooming, usually after winter but really at any time you notice the need. If truly dead (rather than just damaged), the old fronds will pull away from their crown(s) quite easily. Rather than causing damage, this is really of benefit to the plant as dead foliage in the interior can rot and it harbors insects. Look to see how the frond is attached to the fan and pull gently in the opposite (away from the fan crown) direction - it should come off easily and cleanly. The alternative is to cut them off - I prefer the cleaner appearance of pulling - but they do cut easily with pruners.

Thanks for the tips. How much water do you give your flax? Im starting to think I give them too much. Also, do you ever cut the ends of the fronds? I've seen this done (I guess to keep the plant controlled). Is that a good idea/will they grow back?

I don't water very often - either those in the ground OR in containers. They tend to be pretty darn drought tolerant, even the so-called "swamp" species. The fronds can be damaged by wind or traffic and I've seen the tips cut in response to that, but it's not a look I favor. And it wouldn't have any effect on controlling the size of the plants. Fronds cut back for any reason (like for winter or cold damage) tend to look ugly and mangled until they die and are removed from the plant :-)