The idiom "to take down the enemy" means to defeat or kill the enemy, usually in a fight, battle, or confrontation. The phrasal verb take down here signals bringing an opponent to defeat or destruction, not a literal physical action of removing something from a wall.
Option 1 reads the phrase in a completely literal and unrelated sense involving pictures on a wall, which has nothing to do with the idiom. Option 3, making friends with the enemy, is the opposite of the idiom's aggressive meaning. Option 4, to ignore the enemy, also contradicts the sense of direct confrontation and defeat that take down implies.
Since the idiom is used in contexts of combat or competition to describe defeating or killing an opponent, option 2 is correct.