37 C.F.R. § 2.183

A complete renewal application must include:

(a) A request for renewal of the registration, signed by the registrant or the registrant's representative;

(b) The fee required by § 2.6 for each class;

(c) The additional fee required by § 2.6 for each class if the renewal application is filed during the six-month grace period set forth in section 9(a) of the Act;

(d) If the renewal application covers less than all the goods, services, or classes in the registration, then a list specifying the particular goods, services, or classes to be renewed.

(e) If at least one fee is submitted for a multiple-class registration, but the fee is insufficient to cover all the classes and the class(es) to which the fee(s) should be applied are not specified, the Office will issue a notice requiring either the submission of additional fee(s) or an indication of the class(es) to which the original fee(s) should be applied. Additional fee(s) may be submitted if the requirements of § 2.185 are met. If the required fee(s) are not submitted and the class(es) to which the original fee(s) should be applied are not specified, the Office will presume that the fee(s) cover the classes in ascending order, beginning with the lowest numbered class.

(f) Renewals of registrations issued under a prior classification system will be processed on the basis of that system, unless the registration has been amended to adopt international classification pursuant to § 2.85(e)(3).