Most people get very nervous when the subject of changing tension settings is broached. Mastering the ability to change the tension on your sewing machine will broaden your horizons in your sewing career. It will allow you to sew with many different types and weights of thread and will allow you to add new specialty techniques to your sewing toolbox. The following instructions are based on using the same weight of thread top and bottom.
There are two places where the thread tension can be changed on a sewing machine. The main one is the tension dial on the top of your machine and the second one is the tiny screw on the bobbin case. The first thing to know about tension is that you must raise the presser foot when you thread your machine. When the presser foot is down, the tension discs are closed and the thread cannot be properly seated between them. When you want to change the upper tension, place the presser foot in the down position so that the discs are closed onto the thread. To repeat: raise the presser foot to thread and lower the presser foot to change.
The above illustration of a bobbin case shows the adjusting screw and once again, righty tighty and lefty loosey. The adustment would be the exact opposite of the adjustment of the upper tension dial. If the thread is being pulled to the underside, the bobbin tension is too tight so loosen it by turning the screw 1/4 turn to the left and vice versa if the thread is being pulled to the top side. Always make your bobbin tension adjustments one quarter turn at a time and then test it before turning it further. The screw is very tiny and very short. To be safe it is best to change the tension inside of a plastic bag so that if your screw falls out, you can find it again. One of my dear friends dropped her screw in class recently and several of us were climbing around on the floor looking for it. Fortunately we did find the screw and I was able to put the bobbin case back together for her.