oracle多实例的情况下如何进实例

[xx_svr:/app/oracle]$export ORACLE_SID=instancename1
[xx_svr:/app/oracle]$sqlplus /nolog
SQL> conn /as sysdba;
SQL> select name from v$database;
NAME
------------------
instancename1
SQL> alter user sys identified by abc123;
User altered.
SQL>