Once your domain has expired you will not be able to renew it from the Customer Area. However, you can still reactivate most domains during a 27 day grace period at a regular renewal price. You will need to Open a Ticket with customer services to change the status of the domain so you can renew it.
After expiration, domain name can be reactivated for 1 year only.
If the domain cannot be renewed then it has most likely passed the expiration grace period and is now in the redemption period.