We read in Acts 13:42, 44
42) And when the Jews were gone out of the synagogue, the Gentiles besought that these words might be preached to them the next sabbath.
44) And the next sabbath day came almost the whole city together to hear the word of God.
Please note that the Jews gathered together on the seventh day of the week [Saturday] and also note the term "next" in Strong's Concordance means "between" therefore, in this case, "next/between sabbaths" would mean the day after Saturday will have to mean Sunday the first day of the week.
Now the most significant and profound Scripture reference concerning the change from Saturday Sabbath to Sunday Sabbath worship [which BTW, can't be seen in the English translation] is Matthew 28:1 that reads:
"In the end of the sabbath as it began to dawn towards the first day of the week came Mary Magdalene and the other Mary to see the sepulcher."
Please note that the printer is warning the English reader that words in italicize in the KJV Bible, are not in the original manuscripts. Also note that the word "week" is the plural Hebrew word "sabaton" that can be proven.
Hence, Matthew 28:1 can be rendered thus:
"In the end of the sabbaths as it began to dawn towards the first of the sabbaths came Mary..."
Now Matthew 28:1 seems to be in harmony and that God teaches us that He changed the Seventh Day Sabbath Worship to the First Day Sabbath which to us is Sunday.
To God Be The Glory