Open SQL Developer and perform the following steps:
Right click on Connections > New Connection.
Connection Name: sys
Username: sys as sysdba
Password: sys (or your sys password)
Hostname: your database server IP
SID: your sid
Expand Other Users, and choose the user with the expired password. Right click on the user and choose Edit User, enter the new password and confirm it.
If you want your password to never expire again uncheck Password expired (User must change next login).
If you want password never expired, execute following command:
ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;