How to swap head

For the head part, you should delete everything but head part.

1. Make sure it’s bone select mode (B at the top), then show hidden bones (gray circle) and double click head bone. This should select head bone and its children.

2. hide body part with Refine/Masking, then Delete/Erase Hidden Parts.

3. click View Selected in BONE, and click BN-BDY & BDY-JNT.

4. then, delete hidden bones, rigidbodies and joints by inverting visibility with R.

Do the same thing but inverse for the body part, then import head part.

credit: にがもん式霊夢