update PSOPRDEFN@HR89XXX OPXXX
set OPXXX.OPERPSWD = ( select OP.OPERPSWD
from PSOPRDEFN OP
where OPXXX.OPRID = OP.OPRID
),
OPXXX.ACCTLOCK = 0,
OPXXX.LASTPSWDCHANGE = SYSDATE
where OPXXX.OPRID = 'USERNAME'
Along with changing the password you also need to set the last password change date, LASTPSWDCHANGE equal to the current date. Otherwise you could change your password, but have it expire on you immediately.
It also makes sense to reset the account locked flag, ACCTLOCK, in case the account has been locked.