Domain names are similar to a licence.
As you hold the domain name licence you can do what you want with it. All domain names we register are registered in the customer's name. This means that for the duration of the registration period YOU are the licence holder of the domain name.
When the licence is due for renewal, you will have to pay a renewal fee. If you do not renew the licence, then it will become available for any eligible applicant to register on a first come first served basis on the Domain Open Market. This is why it is very important to pay your renewal fee for your domain name every year before the due date. If you don't you will get caught out and lose the rights over your Domain Name and you will also lose the use of your website.