Sze, what kind of Fritz are you useing, and have you tried helping it? My Fritz 12 agree on 1... C5 even shredder on my Phone goes for c5..:)
Speaking of the positional advantage (especially after Aziridines nice explanation) I actually believe you can see the advantage, but not how to win, which probably is difficult against a though opponent. The best tip I have on winning is actually to play the position, then you'll hopefully also see how great the advantage is too;)

Azi, the puzzle is from a book called: Critical moments in chess. By Paata Grapindashvili. Whether the position is from a real game I don't know.
On your puzzle I believe the answer is:
1.Kc8. B5
2. Kd7. Bf5+
3. Kd6. B4
4. Ke5 and then whit gets the pawn on b4 since black need to rescue his bishop.