To do this, simply toggle the iCloud Music Library option off. So if you're precious about your existing downloads (and rightly so), you may want to turn off iCloud. Apple will match these with its own tracks so you can listen offline – but it may not always get the right version. This can present some problems to users with a big existing library, especially if you have your own playlists. In your iPhone/iPad, go to Settings > Music and toggle iCloud Music Library on. A number of features are only available with iCloud Music activated – most notably offline listening. You might want to enable iCloud Music Library to get the most from Apple Music if you're using an iPhone or iPad.
Sign in to iCloud Music for extra features.