You can change the name of your shop at Settings > Webshop Settings.
Your company name and personal information can be changed at Settings > Account settings.
You can change the heading of your invoices and packing slips at Settings > Invoices.
A domain name can not be modified. You can add a new domain name at Settings > My domain names. Your old domain name will automatically expire after 1 year if you do not renew it.
Double check that the domain name you want to register is correct: changing your domain name after registration is not possible! Domain names are reserved and registered in real-time. Registries do not allow domain name changes afterwards. You can however register a new domain name.