Depends on whether you want to keep and reuse or not.
Easiest way of course is to simply jemmy it off the wall with a bar.
If however, you want to do less damage then look carefully for surface imperfections below the rail and these will most likely be the fixings . Digging around there with a small old screwdriver should reveal the fixings which can then be removed with minimal damage. Chances are it's fixed with screws which hopefully will unscrew. It amay however be nailed and you may find it easier to punch them straight through the handrail.
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