Most white cards are only valid for 6 months. That means every half a year you need to go to the Regional Asylum Office which is responsible for you and renew your card. You can find a list of the addresses of the Regional Asylum Offices here:
Everybody whose white card needs to be renewed needs to come in person to the Asylum Office. This also means that if you have little children you need to bring them, in order for their white cards to be renewed too. You can find the expiry date on the right side of the white card. There are two dates written. The date on the top is the date when you have an appointment with the Asylum Office, for example if you have your asylum hearing. Please always also go to this appointment! The second date is the date when your white card expires. The earliest date you can renew your white card is 6 days before and at the latest one day after the day of expiry. If you can not go to renew the card because you are sick, you will need to provide a statement from a doctor proofing that. In case you forget to renew your card, your case will be closed and you will have to ask the Asylum Service to reopen it. According to Greek law, you may only have your case reopened once and this must be within 9 months of it being closed, otherwise the procedure will become more complicated.