Small-angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu2OSeO3. In the absence of an external magnetic field, helical spin order with magnetic modulation vector q parallel to < 001 > was identified. When a magnetic field is applied, a triple-q magnetic structure emerges normal to the field in the A phase just below the magnetic ordering temperature T-c, which suggests the formation of a triangular lattice of skyrmions. Notably, the favorable q direction in the A phase changes from q parallel to < 110 > to q parallel to < 001 > upon approaching T-c. Near the phase boundary between these two states, the external magnetic field induces a 30 degrees rotation of the skyrmion lattice. This suggests a delicate balance between the magnetic anisotropy and the spin texture near T-c, such that even a small perturbation significantly affects the ordering pattern of the skyrmions.