PAL has nothing to do with DVD regions. A DVD can be PAL or NTSC, and completely unrelated to that, it can be restricted to a region or region free.
If it is restricted to a region, you need a DVD player that can play that region. Some DVD players can play all regions.
But you cannot change the disc itself. Of course, if it is not copy protected, you can copy it and make the copy region free (though it will still be a PAL DVD). However, most discs that are for a specific region are also copy protected.