In fixed pawn positions, sometimes a King can outmaneuver the other and win the enemy pawn. This technique is known as "outflanking". It's important to remember that fixed pawns have their own critical squares.
Each pawn has up to three critical squares to the right of itself along the same rank it occupies, and up to three squares to the left on the same rank.
So a fixed pawn in the center could have as many as six critical squares.
If the King can occupy any of the enemy fixed pawn's critical squares it can win the pawn by force.
In this position the enemy's b6-pawn's critical squares are: c6, d6, and e6. To win Black's b6-pawn, White's King simply has to get to the e6 square to outflank Black's King.