To change sys user password in Oracle in Oracle follow these steps:
1. Run Rman.exe from the oracle_homebin directory.
2. On prompt type
Connect Target [and press enter]
SQL "Alter user sys identified by newpsw"; [press enter]
3. Password has been changed. Exit the rman by exit or quit command.
Using Sys Account in SQL*Plus
sqlplus /nolog
connect / as sysdba
ALTER USER sys IDENTIFIED BY "new_password";