conn / as sysdba
alter user sys identified by "P@ssw0rd";
conn sys/"P@ssw0rd" as sysdba

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE    11.2.0.2.0      Production
TNS for 64-bit Windows: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production

SQL> conn / as sysdba
Connected.
SQL> alter user sys identified by "P@ssw0rd";

User altered.

SQL> conn sys/"P@ssw0rd" as sysdba
Connected.
SQL>

SQL> connect sys as sysdba
Enter password:
ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified

SQL>

SQL> alter user michel identified by "P@ssw0rd";

User altered.

SQL> conn michel
Enter password:
ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified


Warning: You are no longer connected to ORACLE.
SQL> conn michel/"P@ssw0rd";
Connected.

SQL> alter user michel identified by "&'()";

User altered.

SQL> conn michel
Enter password:
Connected.
SQL>

SQL> password
Changing password for MICHEL
Old password:
New password:
Retype new password:
Password changed
SQL> conn michel/"P@ssw0rd";
Connected.
SQL>

mydb@mysrv =
  (description =
    (address = (protocol = tcp)(host = itmyserver)(port = 1521))
    (connect_data =
      (SERVICE_NAME = rmcatdev)
    )
  )

C:\Users\estevens\Documents\sql>sqlplus estevens/*****@mydb@mysrv

SQL*Plus: Release 12.1.0.1.0 Production on Mon Mar 16 12:42:02 2015

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Release 11.2.0.4.0 - 64bit Production

SQL>