You can identify your current registrar in several ways. If you remember the company to which you paid your original domain registration fee, contact that organization directly. You can also identify your registrar by looking up your domain name in the public WHOIS database using any WHOIS search tool.

Your domain record includes the name of your registrar, publicly available contact information associated with your domain name, and your domain registration and expiration dates.

There are a number of free WHOIS search tools, such as Tucows'. Just type in your domain name and press enter to see the results - your registrar will be displayed below your domain name: