You need to :
SQL> alter database commit to switchover to physical standby with session shutdown;
Quote ( source - Page 15 MAA - Switchover and Failover Best Practices )
On the primary stop all but one instance (as stated by 11gR2 documentation) srvctl stop instance -d ...
If the production and standby databases are in an Oracle RAC configuration, first shutting down all but one of the production instances. Once the primary database has only one instance up then shut down all standby instances except the apply instance (this will leave a single instance running on each cluster).