How did Hinduism change from the Aryans to the Gupta?

By this I assume you mean the period from roughly 1500
BCE, which signals the end of the Indus Valley Civilization, until the rise of the Gupta
Empire in the 4rd-6th centuries CE. This is a span of time that covers roughly 2000
years and contains some of the most important formative moments in Hindu
history.

First, the Vedas were developed in the period
1500BCE-800BCE. These collections of hymns and mythology were intended to accompany
complex rituals. The brahman priests performed these rituals,
chanting the Vedas to the gods, thus maintaining the cosmic
harmony.

But the Vedic rituals were complex, expensive, and
difficult. Commentaries on the Vedas began to teach that one should worship the gods
within, through meditation, fasting, and prayer. The Upanishads mark this change in
orientation. These texts taught that one's true Self, the immortal
atman, was divine in nature and that through yoga and meditation
one could lose oneself in divine union.

A third major
religious movement developed in this period in Hinduism. Many of these teachings (of
Vedic rituals, of sacrifice, of losing oneself in God) were often reserved for upper
classes and/or people who left society on a spiritual quest. But in the period
200BCE-200CE the great epics, the Ramayana and the
Mahabharata presented many of these ideas in a popular format with
stories of heroes. In particular, the Bhagavad-Gita that all people
should act selflessly, performing their caste duties, and live in virtuous devotion to
God. So this third movement may be described as a popular movement, a way of making
these earlier teachings more publicly available.

By the
way, it used to be thought that India was subject to invasions by people called the
Aryans. In recent decades, this idea has been largely abandoned. Although a few scholars
current in the field still believe the Indus Valley Civilization fell to some Aryan
invasion, there is little evidence to substantiate this idea.