Navigate to the Web-RAR tab on the left sidebar, under Domains, select the domain you wish to renew. Ensure you have ample funds and then renew your domain. https://portal.dns.business/webrar/gateway/home_new#myDomainsView
Please also note that you can set an auto-renew status for your domains and the domain will renew automatically. You will need to ensure you always have sufficient funds in your account for the renewal to take place.