Lenova vibe K4 note

Hi Guyz,
From last 4 months I am using lenovo k4 not, recently I upgraded to marshmallow from lolipop. the worst experience with android 6.0 , mobile heating more than before, battery also draining fast. 2. 25GB RAM consuming and affecting on performance. now I want to downgrade to android 5.1. please give some best option for this.

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