How to alter the password expiration policy for certain user.

To alter the password expiry policy for a certain user profile

in Oracle first check wich profile the user is in using:

select profile from DBA_USERS where username = <username>;

Then you can change the limit to never expire using:

alter profile <profile_name> limit password_life_time UNLIMITED;

If you want to previously check the limit you may use:

select resource_name,limit from dba_profiles where profile='<profile_name>';