There are a bunch of articles on steemit that talk about different ways to do that. You can use the Steemit custom Google search (click the magnifying glass in the header to get to the search function), or just use Google. I searched here, and found this article which may be helpful: https://steemit.com/steemit/@ratel/instructions-for-those-who-want-to-withdraw-their-steem-to-bitcoin Look at step 3.