How do I delete tracks from my account?

To delete a track on your profile, hover over the waveform and click on the trash can icon that appears like this: 

On the Tracks page (https://soundcloud.com/you/tracks), the trash can appears on the right side of the title:

Please note: deleting a playlist you have created will not delete the individual tracks within it that have been uploaded to your account. In order to make more room you will have to delete the individual tracks.