Hi Richa,
If you use SAP Authentication, make sure that new BW Server application server/message server detail's are updated.
If the system name changes (ex: Change the system name to HBD to HBQ), then all the users needs to be imported again.
If you message server in Connection, you have to update SAPGW number of the BW system in the services files of Windows. Hopefully your BASIS team will have those entries.
if you use Application server details in the connection, then no need to update the same.
Hope this answers your question.