Having cleared a family attic I have found 2 old singer sewing machines how do I dispose of them ?

What condition are they in?
If they are in decent enough condition you can donate them to the Goodwill or some donation place like that.
You could also put an ad in the paper and try to sell them.
If they are in really unrestorable condition you can put them out for the garbage on bulk night.

If they are really old as in antique and in good condition, they might be worth something. I see them being sold all the time.