Changing node type of data nodes for a 3 node cluster with high RAM usage to master-data node

[elastico]

I have a three node cluster with 1 master-data node and 2 data-only nodes. I want to make this into a 3 master-data node cluster. To this effect, I need to change config for the data nodes one at a time and restart them. However, cluster is showing high RAM percentage for all three nodes.

I have read elsewhere that ES usually has a high RAM usage so as to increase performance and will reduce its RAM usage if need be.
Would it be safe to take an instance out and restart it, without adding another data node to handle the load in the meantime.

[warkolm (Mark Walkom)]

Please don't post pictures of text, they are difficult to read and some people may not be even able to see them.

You are totally ok to shutdown one node at a time to do this, check out https://www.elastic.co/guide/en/elasticsearch/reference/6.4/rolling-upgrades.html for the process that can be applied.

[elastico]

Thanks