Launch iTunes. Go to "File" and then "New Playlist."
Drag the M4P files into the new playlist.
Insert a blank recordable CD in your disc drive.
Click on the playlist and then click on the "Burn Disc" button that will appear in the bottom-right corner.
Select "Audio CD" next to "Disc Format" and click the "Burn" button. After iTunes burns the files to CD, it will eject the CD.
Insert the CD back in the disc drive. iTunes will scan the disc and ask whether you want to import the CD. Click "Yes." The songs will now be burned back into your library without any DRM attached to them.