Can I file an amendment to my original application or do I have to file a new application?

You can file amendments, but the kind you are looking to file are probably not going to be allowed. You are probably better off just filing another application with the new logo listing all your goods and services.

Section 1402.06 below, from the TMEP (Trademark Manual of Examination Procedure) available online apparently answers your question(s). Regards, dan 1402.06 Amendments Permitted to Clarify or Limit Identification Trademark Rule 2.71(a), 37 C.F.R. 2.71(a), restricts amendments to the identification of goods or services as follows, "The applicant may amend the application to clarify or limit, but not to broaden, the identification of goods and/or services." This rule applies to all applications. Section 7(c) of the Trademark Act, 15 U.S.C. 1057(c), provides that filing an application for registration on the Principal Register establishes constructive use and nationwide priority contingent on issuance of the registration (see TMEP 201.02). Therefore, the identification of goods and services in an application defines the scope of those rights established by the filing of an application for the Principal Register.