The first if the current user is root, then the first switch to the Oracle user, and then open sqlplus, and give dba role.
[Oracle @ oa2RedHat ~] $ sqlplus / nolog
SQL * Plus: Release 22.214.171.124.0 Production on Fri Oct 10 16:41:26 2014
Copyright (c) 1982, 2009, Oracle. All rights reserved.
SQL> conn / as sysdba;
SQL> select username, account_status from dba_users;
Get the following menu list, and then find you need a user to see his status, if locked, then execute the following command to unlock
SQL> alter user test account unlock;
Of course, you can also use plsql client tools, remote connection you need to unlock the database, using dba role, and then do the unlocking operation in the graphical interface. So it is relatively simple.