1Run SQL*PLUS using Run SQL Command Line in Oracle Database 11g
2Connect to Oracle Database as SYSDBA as follows:
3
4SQL>connect as sysdba
5It will ask you to enter username. Enter SYS as username. change_on_install as Password
6When prompted for password, enter , which is the password for SYS account.
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8SQL> ALTER USER system IDENTIFIED BY oracle;
9The above command changes password of SYSTEM account to oracle. Be careful passwords are case-sensitive.
10That's all you have to do to change password for SYSTEM account when you forget the password.
11Here is the snapshot of the SQL*PLUS screen, which shows all required steps.