The password that you use to access the front-end and the computing systems (Kerberos 5 Password) will expire after one year at the latest and you will be requested to change it upon your next login on the front-end system.
The procedure to change the expired password is the same as described here: you will be prompted to enter your expired password and then your new password twice.
Users can change their password on the Account and Resources Management Tool. You can find a detailed description of the tool on the dedicated page the CSCS User Portal.