Depending on where exactly you have found your music online there are various things you can do to have it removed.

You can issue a DMCA takedown notice which is an official letter to remove copyright material from the internet that is being unlawfully distributed.

How to Issue a DMCA Takedown Request

In order to issue a DMCA takedown, you need to submit a written notification by a person authorized to act for the copyright/license holder. This needs to include:

• Contact information (including address, phone number, and email).
• The full name of the track/release in question.
• The web address of the track/release in question.
• A statement of good faith belief that the use of the material in question is not authorized by the copyright owner, its agent, or the law.
• A statement that the information in the statement/notification is accurate.
• A statement that, under penalty of perjury, the legal entity is authorized to act for the copyright holder.
• Signature (written or electronic).

Where Do I Issue the DMCA Takedown Request?

Most online stores will have a copyright complaint section or "report abuse" section. It is often found via the home page, towards the very bottom of the sites where they list numerous services and links.

It is best to issue the DMCA directly via the particular site's official channels and in most cases, content is reviewed and removed quickly. If the site does not have a dedicated section for this, then you need to email them directly.