In your Magroove for Artists account go to My Releases and choose the one you want to take down. Click on the settings button (looks like a wheel - check the screenshot to be sure). The whole process might be instantaneous on some stores, but other might take up to only 1 week max.
1 - Global Takedown from every store: under the Basic info tab scroll down to the Danger Zone. There you can choose to only take down the whole release from every store but keep it on our database which would enable you to put them online again in another time. Or choose to delete your whole release from stores and our database, which would require you to upload them again if you wanted them to be online in the future.
2 - Takedown from a specific store: under the Stores tab you can check each and every store that your release is uploaded to. Open the tab for the store you wish to take it down from and you'll se an area called Danger Zone, there you can choose to take down from that single stores while keeping your release online on others.