Did Rosh hashanah change

Yes, in the following ways:

1) When the Temple still stood, the shofar (a kind of Trumpet) was sounded (Leviticus ch.23) even when Rosh Hashanah occurred on Shabbat. Today, if Rosh Hashanah occurs on Shabbat the shofar is not used.

2) When the Temple still stood, sacrifices were offered on Rosh Hashanah (Numbers ch.29).

3) In ancient times, Rosh Hashanah was celebrated for only one day. For a technical reason involving the timely appearance of witnesses to testify concerning the new moon, the sages instituted the celebration of two days for Rosh Hashanah.