Checking iTunes collection for DRM
Delete Old DRM Copies of iTunes Music and Download DRM-Free Versions
If you purchased any music from iTunes between 2003 and 2009, you downloaded tracks with DRM (Digital Rights Management) in them. Apple's long since removed the DRM, but you might not have. Wired shows how to update your music library with the new, DRM-free versions.
The process here is pretty simple, but if you're anything like me, you never bothered to actually do it:

Before starting, make sure you are signed in to the iTunes Store [Store menu] &amp; can see the columns for Kind &amp; iCloud Download in your Songs view in iTunes, then sort by Kind
Scroll down to find 'Protected AAC audio file' as a Kind - those are the ones you need to replace.



In iTunes, select iTunes &gt; Preferences and click the &quot;Store tab&quot;
Make sure &quot;Show iTunes in the Cloud Purchases&quot; is checked and close the Preferences panel
Click on the cloud icon in your list view and make sure all your purchases are there (note which songs are here and do not delete anything in step 5 that isn't available for download)
Now, delete the old DRM versions by sorting by &quot;Kind&quot; in the list view (if it's not there, go to View &gt; Show View Options and select it)
Scroll down to see if any tracks are listed as &quot;Protected AAC audio file.&quot; That's the DRM music you need to replace. If you can download it again from iTunes with the cloud icon, you can delete the DRMed version

Once you run through the process of deleting those songs you can download them from the cloud at any point, DRM free. This has been around for a while, but if you haven't grabbed those DRM free versions, now's as good a time as any.
Source: Lifehacker Delete Old DRM Copies of iTunes Music and Download DRM-Free Versions
Also see - Which songs in my iTunes library are DRM protected?