To convert your existing company-type handle to a reseller handle, log into your handle and go to Account Management, then then select the “Become a Reseller” tab.
If you fulfill the requirements to convert to a reseller (e.g. you are a billing contact for at least one domain), you will be prompted to accept the reseller contract.
You will then be able to import all the domains on which your handle is listed as the billing contact. To do so, click on “reseller options” then “Add domains to my reseller account.” Domains which have your handle as the billing contact will be added automatically.