Why did the pope change the Sabbath day?

I have learned in the year 321AD at the council of laodicea the pope of the day and the ruler Constantine changed the Sabbath that God had set as the 7th day (Saturday) since creation until apparently 321 ad when the Pope changed it.

Why did he change it?

Does he have the authority to change one of the 10 commandments?

Thanks in advance, James:)

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