How to increase max file descriptors in elasticsearch

max file descriptors [4096] for elasticsearch process likely too low, consider increasing to at least [65536]---I am getting this warning..

I have added MAX_OPEN_FILES=65536 in bin/elasticsearch file...but I am unable to overcome this warning...

I feel the process is very slow as I am indexing very large data into elasticsearch.

Thank You

What OS?

Cent OS