The "feet" on the bottom of each leg are adjustable. You should have received a special pressed-metal wrench to turn the big nut on the bottom of each leg. Or, you can use a monkey wrench. Think about righty-tighty, lefty-loosey, only upside down. So.... counter-clock-wise will lower the frame, and clock-wise will raise it. You don't need a level to check if you're straight. Just gently roll the sewing machine to see which way gravity is pulling it. Check it forward/backward and side to side, then adjust the feet up or down as needed for each leg.