Hello,

Take a look at section 307 Time for Filing Petition to Cancel 15 U.S.C. 1064 [Section 14 of the Trademark Act]

A petition to cancel a registration of a mark, stating the grounds relied upon, may, upon payment of the prescribed fee, be filed as follows by any person who believes that he is or will be damaged, including as a result of dilution under section 43(a), by the registration of a mark on the principal register established by this Act, or under the Act of March 3, 1881, or the Act of February 20, 1905:

(1) Within five years from the date of the registration of the mark under this Act.
(2) Within five years from the date of publication under section 12(c) hereof of a mark
registered under the Act of March 3, 1881, or the Act of February 20, 1905.
(3) At any time if the registered mark becomes the generic name for the goods or services, or a portion thereof, for which it is registered, or is functional or has been abandoned, or its registration was obtained fraudulently or contrary to the provisions of
section 4 or of subsection (a), (b), or (c) of section 2 for a registration under this Act, or contrary to similar prohibitory provisions of such prior Acts for a registration under such Acts, or if the registered mark is being used by, or with the permission of, the registrant
so as to misrepresent the source of the goods or services on or in connection with which the mark is used. If the registered mark becomes the generic name for less than all of the goods or services for which it is registered, a petition to cancel the registration for only those goods or services may be filed. A registered mark shall not be deemed to be the generic name of goods or services solely because such mark is also used as a name of or to identify a unique product or service. The primary significance of the registered mark to the relevant public rather than purchaser motivation shall be the test for determining whether the registered mark has become the generic name of goods or services on or in connection with which it has been used.
(4) At any time if the mark is registered under the Act of March 3, 1881, or the Act of February 20, 1905, and has not been published under the provisions of subsection (c) of section 12 of this Act.
(5) At any time in the case of a certification mark on the ground that the registrant
(A) does not control, or is not able legitimately to exercise control over, the use of such mark, or
(B) engages in the production or marketing of any goods or services to which the
certification mark is applied, or

(C) permits the use of the certification mark for purposes other than to certify, or

(D) discriminately refuses to certify or to continue to certify the goods or services of any person who maintains the standards or conditions which such mark certifies: Provided, That the Federal Trade Commission may apply to cancel on the grounds specified in paragraphs (3) and (5) of this section any mark registered on the principal register established by this Act, and the prescribed fee shall not be required.

I think it costs something like $300 to file.

Look at this link, read the stuff, outlines the procedure

http://www.uspto.gov/go/tbmp/300.pdf