as said above. your machine may not have the down position. But check to see if your foot control will make the need stay up or down if you tap on it. Some machines do.
If your machine does not have the down button, then be sure your hands stay on the quilt when you stop so it won't move as you change positions. Turn the hand wheel to put the needle down so it will hold the quilt while you hange positions. And go slow. And then hold the quilt in position and take a stitch or two in position until you have control with your hands. This will help in not letting the quilt jump when you start again.