Although you own the domains you register, you can’t delete them from their respective registries. If you no longer have a use for a domain, you can just let it expire.
To do that, go to your ScalaHosting Client Area, open the My Domains section, and locate the domain you no longer need to use. Make sure its auto-renewal is disabled.\
Shortly after it expires, the domain enters a redemption period that gives you the option of restoring it. If you let the redemption period pass, the registrar will eventually delete the domain and make it available for registration once again.