Elastic Log data transfer in remote server

I have 3 node cluster
all three node have same configuration
node.master: true
node.data: true

so now my storage i filled up almost 800GB. I want to transfer some data for future reference from the path : /var/lib/elasticsearch
#May i need to transfer from all 3 node ?

What i need to do to free up my disk space ?

If i transfer incides from the path from one node is it okay .
is there any automated or manual process ?