Mukesh,
Hal Ruggles pointed out something that was missing from some other replies: the Java Config Tool. We recently completed a database upgrade to MS SQL Server 2012, which resides on a new database server, so we also had to copy the old Portal database to the new server.
After backing up our database we made one change in the Java Config Tool: go to Secure Store > Connection Pools > <SID> Properties. For Key = "Url", update the value with your new database name -- e.g. Value = "jdbc:sqlserver://<your_database_name>;databasename=<SID>".
After restoring the backed-up database to the new database server, we made the appropriate changes in the Default Portal Profile. The parameters we had to change were SAPDBHOST, j2ee/dbhost, and dbs/mss/server.
The only other place we found needing the new database name was our developers' NWDS settings.
I hope this helps.
Best regards,
Jill