Oh, okay, that's a pretty simple machine and might be easy to figure out. :)
Try turning the tension dial a couple of numbers lower and see what that does. Then turn it a couple of numbers higher and see what that does. If there is no difference either way, the thread is possibly not seated properly between the two disks or the disks are sticky.
If the stitching gets better when you turn it a little lower and the stitching on the back still looks good, keep turning it lower and testing until the stitching on the back starts getting loose or loopy. At that point, the tension is too loose, so you would tighten it back up to the loosest setting that gives you a balanced stitch on both sides of the fabric.
It's possible that the tension on your bobbin case is too low and you may have to tighten that up. There are directions in your manual. If you have a removable bobbin case, I would recommend cleaning out the tension spring on the bobbin case before setting the tension. Even a tiny bit of old lint/oil can keep the spring from applying enough tension to the bobbin thread, even when you tighten the tension screw all the way down.
Just some things to check out. Let us know what you try and what the stitching looks like. :)