"Changing my diet was the big thing," the 5-foot-7 Georgia native tells the new issue of Us Weekly (out now). "I had to learn correct portion control."
The singer (her first disc, Wildflower, debuted at No. 5 on the Billboard Top 200 albums chart) initially used the meal delivery service Sunfare to transition into a high-protein, low-carb diet.
Daily workouts of crunches, pushups and "lots of squats have also helped, the size-2 singer tells Us. "I'm 10 pounds from my goal -- almost there! I wear size small and extra-small now!"