Depends on how unlevel it is. If you want a permanent soluction, you can find a floor leveling compound at a home improvement center. If you want something quick and easy, you can buy some wood shims. A shim is a piece of wood like a wedge that you can stick under the tank stand to raise a section of the stand. You might want to use a level to make sure the stand is level and check it both ways, across the front and then from front to back.