If your domain name is registered with KartHost.com please read this KartHost Knowledgebase Article "My Domain Expired Can I Get it Back - Domain Renewal Grace Period"
However, if your domain name is registered at another Domain Name Register, unfortunately KARTHOST will not be able to help you, you will need to contact the Registrar that your domain name is registered with and renew the domain name as soon as possible, before the domain slips into Redemption Grace Period.
If you need help please open a KartHost Domain Name Support Ticket!