Take a small stick ... like a coconut leaf twig (or what ever they are called), slowly twist it at the algae. It should curl on to the stick and you can pull it out. This only reduces, it doesn't eliminate them.
If possible, slowly take the plants out - careful, fry might get caught in them. Then cover everything - no light at all 24/7. This should reduce the algae if not kill it. Then siphon it out. If you don't take the plants out, they will also die and you will at least have problems of cleaning the tank floor.
I usually throw away all plants that have been infested by hair/thread algae. No matter how you clean them, algae will regrow. If you don't have anymore plants, put them in a bucket and let them grow. Pick out the new stems (1cm long) and let it grow in a clean, algae free water. It may take a few weeks, but you will still have plants. ..... Oh, btw, I was talking about stem plants, not large leafed plants.