Swami Adiswarananda states that in a human body alone can
one change karma. Swami Adiswarananda (1925 – 2007) was associated with the
Ramakrishna Mission.
From the viewpoint of Hinduism, heaven and hell are merely
different worlds, bound by time, space, and causality. According to Hinduism,
desires are responsible for a person's embodiment. Some of these desires can
best be fulfilled in a human body, and some in an animal or a celestial body.
Accordingly, a soul assumes a body determined by its
unfulfilled desires and the results of its past actions. An animal or a
celestial body is for reaping the results of past karma, not for performing
actions to acquire a new body.

Performance of karma to effect any change of life is
possible only in a human body, because only human beings do good or evil
consciously.
Human birth is therefore a great privilege, for in a human
body alone can one attain the supreme goal of life.
Thus, in search of eternal happiness and immortality, the
apparent soul is born again and again in different bodies, only to discover in
the end that immortality can never be attained through fulfillment of desires.
The soul then practices discrimination between the real and the unreal, attains
desirelessness, and finally realizes its immortal nature.
Affirming this fact, the Katha Upanishad says: "When
all the desires that dwell in the heart fall away, then the mortal becomes
immortal and here attains Brahman."
Swami Adiswarananda (1925 – 2007)