The easiest way to redeem your coins is to do it from steemit.com. If you're not logged in there, then use the same keys as here on Musing. You will only need the Posting Key to claim your founds, but the Active Key in order to transfer them to another user, such as an exchange. 

Anyway, when you're on Steemit, go to your user profile, then click on "Wallet". There's a big button that allows you to claim your funds there. You get 50 % of the money as STEEM, and the other part as vested STEEM, more commonly known as Steem Power. You can power this down if you want to sell it, but it will take a total of 13 weeks to get them all into liquid form. 

Just keep in mind that funds can only be claimed one week after your originally posted your question / answer. The same rules apply here as they do on all other Steem apps, so it should be easy to understand if you are already familiar with Steemit.