Hi Ashish,
It is recommended that the Explorer upgrade should happen immediately after BI 4 upgrade. Hence I would suggest to upgrade Explorer to 4.1 SP2 immediately after BI Platform 4.1 SP2. The changed order should be as follows.
Install Platform 4.1 SP2 on primary server
Install Platform 4.1 SP2 on additional servers (parallel on all app server)
Install Explorer 4.1 SP2 on primary server
Install Explorer 4.1 SP2 on additional servers (parallel on all app server)
Install Platform 4.1 SP4 on primary server
Install Platform 4.1 SP4 on additional servers (parallel on all app server)
Install Explorer 4.1 SP4 on primary server
Install Explorer 4.1 SP4 on additional servers (parallel on all app server)
Then follow the same order as above for Patch 3 upgrade.
Regards,
Hrishikesh