Magnetic phase diagram of a material could be tuned through structural modication. Here we show significant lowering of magnetic field (Hi) required from transition from cycloidal to canted antiferromagnetic state in sheet like nanostructures of BiFeO3 (BFO), in comparison to reported bulk single crystals of BFO. Structural analysis of this sheet like nanostructured BFO suggests that there is more tilting in FeO6 octahedra that reduce Fe-O-Fe distance in comparison to bulk BFO, leading to decrease in Hi through the reduction of exchange interaction strength.