Use FNDCPASS to change passwords

# change the apps password
FNDCPASS apps/apps 0 Y system/manager SYSTEM APPLSYS newappspassword

# change non-apps passwords
select 'FNDCPASS apps/apps 0 Y system/manager ORACLE '||oracle_username||' '||'newpassword;' from fnd_oracle_userid
where oracle_username not in ('APPS','APPS_MRC','APPLSYS','APPLSYSPUB','CTXSYS','EDWREP','PORTAL30_SSO','PORTAL30');

# change a user password
FNDCPASS apps/apps 0 Y system/manager USER sysadmin newpassword