Digital Millennium Copyright Act (DMCA) is United States Copyright Law that lets elimination of those files that are being used with or without prior permissions of Owner of that particular website. For the purpose of filing complaint, you need to follow these steps:
First, collect URL(s) of offensive file(s)
For example, URL can be like,

Note: We are not hosting such file(s) anymore.
Secondly, you must ensure that you are genuine owner of this website and this file deserves no permission to be utilized on this site. For proper and successful processing of DMCA, you will have to send e-mail from that domain that is owned legitimately by offended company. Plus, keep in mind that DMCA complaints are not accepted from Gmail, Yahoo, Hotmail, or any other free web mail accounts.
Thirdly, you now will prepare email for sending here:
Fourthly, you must ensure that subject of email is written as “DMCA”( Company name) like ( DMCA & XYZ)

Plus, this email should consists of identification of copyrighted works, material location(s) of copyright infringing and also detailed statement of authority.