Unfortunately, the account name that you select at the time of registration (e.g. acme.egnyte.com) cannot be changed.
If you wish to change your account (also known as a domain) name, you'll need to register a new account and transfer your files to this new account.
You can, however, customize your Egnyte account to utilize any URL you choose, including one that utilizes your company's URL. For example, an Egnyte account can be named fileshare.acme.com instead of acme.egnyte.com. The new website address will be displayed in the Web UI, and all the Egnyte Share Links. See Egnyte Custom URLs for more details.