If it is the Star Grass - Heteranthera zosteraefolia on the far right not behind the driftwood - I usually pull the whole lot out, chop off about half the length, then replant it. (Usually by laying the stalks down and sticking a rock on top of them)
This means that you have the nice top growth showing all the time.
If you are not concerned about how it looks, you could just cut it down by two thirds and wait for it to regrow, do this selectively so that you have some top growth showing above the hacked off bits, rather than just a bunch of stalks.
Don't be too conservative with your trimming if things are growing really well, otherwise you will end up with top heavy plants where they branch off and multiply where you have trimmed them, and get all leggy at the bottom because they get no light.