Sewing Machine Dropped Needle Calamity

I was making a couple of peg bags recently when I came across a problem with my sewing machine.  I admit my knowledge of sewing is limited, particularly with sophisticated all singing, all dancing machines such as the fabulous number donated to me last year.  This one is so much more exciting than anything I have ever used before that I’m still working through all the options available to me.    All was going well until I changed the needle, as instructed after so many ’rounds’ when my poor arthritic fingers let go of the old needle and it disappeared down through the throat plate down into the bowls of the bobinn casement.   I cannot find a way of undoing the upper screw mechanism to release it and I think the needle is interferring with the smooth sewing. This is where we take the machine to a professional service centre to be cleaned and sorted!  The orignal owner of said beauty had it serviced every year without fail and I shall definitely be following suit.