Source : Webster's Revised Unabridged Dictionary (1913)

Unlearn \Un*learn"\, v. t. [1st pref. un- + learn.]
   1. To forget, as what has been learned; to lose from memory;
      also, to learn the contrary of.

            I had learned nothing right; I had to unlearn
            everything.                           --Milner.

   2. To fail to learn. [Obs.] --Dr. H. More.

Source : WordNet®

unlearn
     v 1: try to forget; put out of one's memory or knowledge
     2: discard something previously learnt, like an old habit
     [also: {unlearnt}]