See the given image carefully. What you have to do is move the blue checkers in the position of the black checkers and vice versa. You are only allowed to move the checker to an adjacent empty space. Do it in the least possible moves.
1 -> 4
6 -> 1
2 -> 6
5 -> 2
4 -> 5
Of course, you can do in a different manner, this is just one of the possible solution with least number of moves.