Can I change my domain name after purchase?
No, you cannot change your domain name after you buy it.
When you buy a domain name, it belongs to you till after one year (or the period which you registered it for). It is similar to renting an apartment. You cannot change an apartment after you rent it for a year unless you find someone else who is interested in that same apartment then you can (sublet to the person), although in domain names you can sell and transfer the domain to someone who might be interested in buying it from you for the remaining period of registration.
If you want another domain name you need to buy it separately. If you cancel your domain registration after payment and activation, you forfeit the domain and you will not be refunded for it.
