Can the original plaque of self-employed upgrade co., ltd be used?

Yes, you can. According to the laws of our country, you can keep this name. Legal Basis Article 40 Where an individual industrial and commercial household applies for changing its organizational form into an enterprise, the registration authority shall provide it with the convenience of changing the organizational form of the market subject, such as continuing to use its original name and font size and maintaining the continuity of industrial and commercial registration files, as well as relevant policies, regulations and information consulting services. When dealing with it specifically, just add the words limited company after the original name.