According to our tradition, converts acquire a "new soul" in, or upon emergence from, the conversion mikvah. (Not sure of the original source for this--it may be the Zohar--but there are countless secondary sources.) Accordingly, they change their names, and lose most components of halachic relationship with their birth-parents. But is(n't) the "new soul" just a new Jewish soul, a נשמה, in addition to the convert's preexisting nefesh and ruach? Does(n't) the convert keep the nefesh and ruach he was born with? If so, why would the convert's name, and particularly parents, have to change?