you can dowload a manual from the singer website http://www.singerco.com/accessories/manuals.html
If the bottom stitching is uneven, its mostly the top thread not under tension correctly so check the tension dial and the threading up from the thread spool to the needle.
Also, review how you wind a bobbin, you want a nice smooth wind, not twisting or uneven build across the bobbin. The manual for this machine is pretty brief on this but bobbin winding is crucial to getting a good even flow from the bobbin when stitching seams. You want to wind thread smoothly onto the bobbin, across the full width of it, not just mainly in the middle. Give the thread a nudge with your finger tip to fill top and bottom as it winds.
Also, ensure the thread goes through the bobbin tension disc on top of the machine, and even then, use your scissors handle to put some downward gentle pressure onto the thread spool you are winding off so it doesn't jump or bounce as you wind. Wind the bobbin to 3/4 full, then stop.
And lastly, load the bobbin correctly following the manual directions, make sure it is turning the right way in the bobbin case. Also look at page 16, it shows the "dangle" test where you can check the tension on the bobbin case is right, you should be able to dangle the bobbin by the thread tail and it should "stay" but you should be able to pull on it to release thread too. Adjust the little tension screw in minute increments to get this right. Bobbin case tension springs can fail or break too, so check this out.
Hope this helps you; it is my experience that 90% of machine issues are caused by blunt or wrong sized needles, wrong threading, no tension or incorrect tension or lack of maintenance.