There is such a thing as a child theme, but it’s something you create manually to add customisation. In this instance, it sounds like you’ve got multiple copies of the theme installed.
If you go to appearance themes, you’ll see the active theme – appears first in the list- and then the subsequent copies. If you click on one of the inactive versions of the theme, you’ll have the option to delete. Do that on the two copies you don’t need, you won’t need to log in via fpt, you can do it directly from inside the wp admin area.