Use sp_modifylogin to change the password expiration interval for an existing login, add a password expiration interval to a login that did not have one, or remove a password expiration interval. sp_modifylogin only effects login passwords, not role passwords.
This example changes the password expiration interval for the login “joe” to 5 days:
sp_modifylogin "joe", @option="passwd expiration", @value="5"
The password expires 5 days from the time of day you ran password expiration.
The value parameter is a character datatype; therefore, quotes are required for numeric values.
See sp_modifylogin in the Reference Manual: Procedures.