If you’ve been affected by Google’s Penguin algorithm due to unwanted backlinks you’re going to want to create an audit on your digital footprint. Unfortunately there’s no easy way around it; you’ll have to sift through the internet and find all of the unwanted backlinks leading to your site. There are backlink tools available that will create a list of all the sites that are linking to yours. After you narrow down the rotten websites that are backlinking to yours, you’ll want to contact these websites and request that they remove the links. There is no guarantee that the other Webmaster will see (or accommodate) your request, but contacting other websites directly is the best solution for removing unwanted links. If you are unsuccessful with reaching the Webmaster you may ask Google to start disavowing links (Google Support).