Based on your comment, it sounds as if you have an indexer cluster and two search heads. Clustering two search heads is not a supported configuration, so I am going to assume that you just have the indexer cluster and two search heads.
It does not matter when you upgrade the deployment server. You can't upgrade clusters with the deployment server. Use that for your forwarders, which you can have on an entirely separate upgrade schedule.
hi thanks for the link but i just logically wanted to know the steps . We are having distributed clustered environment with two search heads in cluster and two indexers in replication cluster with one deployment Server .