This post can help http://www.seomoz.org/blog/googles-disavow-tool-take-a-deep-breath
There are many free and paid tools that can help determine if you need to delete a link
http://cyrusshepard.com/boom-1-email-60-bad-links-gone-4-tools-for-easy-link-cleanup/
If you understand Spanish this post can help
http://luissobrevilla.com/como-eliminar-backlinks-de-mala-calidad/