You should not need to adjust the tension on the bobbin case for this model at all. The problem is more likely to come from your top thread being insufficiently tensioned if you are getting threads looping on the underside of the fabric.
Here is my trouble shooting suggestions and the general things on threading up apply to most sewing machines.
Check the top threading up, you need the thread to go through all the thread guides but in particular, the thread take up lever and the top tension discs are critical. Always thread up with the pressure foot raised as this opens up the tension discs so the thread can seat in fully. Set top tension dial on 4. Once youve got the thread down to just before the needle, lower the pressure foot and pull the thread, it should be really firm and hard to pull. If it isn't then recheck the threading into the tension device again. If you can't get tension at all, then this device is faulty and will need to be serviced.
Also, if you have never cleaned your tension discs, its a good idea to give them a clean every month or so. To do this, turn tension dial to zero, then "floss" between the discs using the selvage edge of a clean piece of cotton fabric offcut, sometimes you can get build up there of dye particles or thread fibres, especially if you use some cheaper cottons that are very "hairy". Remember to reset tension to 4 when you are done cleaning.
Next, remove your bobbin from the bobbin case and make sure there are no threads looped around the hook or caught in this area. If you can see a stray thread, then unscrew the needle plate (two screws) and take it off. Lift out the bobbin holder, it will come up and and out towards you. Using your little brush that came with your machine, brush out the hook carefully, removing any lint or thread bits. Also check the bobbin case itself and brush it out everywhere and check that no thread piece is caught into the tension spring on the case. Also check the case itself for any damage or piercings from your needle (if the case dislodges during a jam up it may swing and the needle strike it). If there is damage, you can file it out with an emery board.
Replace the case back into the machine, it has a flat side that goes to the back of the machine and a mark which should match up with the stopper in the machine, two red arrows to match.
Now, look at your bobbin, is it wound smoothly and evenly or a bit of a birds nest itself. If it is not an even wind, then pull the thread off, and do it again. The thread needs to come from the thread spool, across to the tension disc on top, then back to the bobbin spindle so it is tensioned as it winds onto the bobbin. Please read my bobbin winding tip here http://www.fixya.com/support/r10598580-winding_bobbin_correctly
for more on this, it is important.
You can now replace your needle plate and screw it down and drop in your bobbin making sure it turns anticlockwise when you pull the thread tail. You always want the thread to come off the bobbin, then reverse direction in a "V'as it comes out of the case. Now take the thread tail around the outside of the bobbin case moving it clockwise until it does into the little groove on the side, then press down on it until it clicks into the tension spring. Pull upwards to check it is into tension. If it comes out again, it wasn't in fully; repeat until it is fully into the spring.
Use your needle up down function while holding the top thread to draw the bottom one to the top, then put the clear cover back in position covering the bobbin.
Try stitching again; please always hold the two threads firmly at the start of a new seam, to ensure the threads don't get pulled down into the hook as this will cause a thread jam.
Hopefully one of the above will resolve the birdsnesting problem, that does really sound like no top tension happening. Feel free to post again if its still not resolved.