It looks to me like the Sabbath is Saturday and that Sunday is the first day of the week.
If that is true, then where in the Bible does it say we can change our sabbath day to any day we like better than the Original?
You REALLY don't know?
I'd suggest you stay off of FR for a week and just read the NT through.
14 Accept the one whose faith is weak, without quarreling over disputable matters. 2 One person’s faith allows them to eat anything, but another, whose faith is weak, eats only vegetables. 3 The one who eats everything must not treat with contempt the one who does not, and the one who does not eat everything must not judge the one who does, for God has accepted them. 4 Who are you to judge someone else’s servant? To their own master, servants stand or fall. And they will stand, for the Lord is able to make them stand.
5 One person considers one day more sacred than another; another considers every day alike. Each of them should be fully convinced in their own mind. 6 Whoever regards one day as special does so to the Lord. Whoever eats meat does so to the Lord, for they give thanks to God; and whoever abstains does so to the Lord and gives thanks to God. 7 For none of us lives for ourselves alone, and none of us dies for ourselves alone. 8 If we live, we live for the Lord; and if we die, we die for the Lord. So, whether we live or die, we belong to the Lord. 9 For this very reason, Christ died and returned to life so that he might be the Lord of both the dead and the living.
And upon the first day of the week, when we were gathered together to break bread, Paul discoursed with them, intending to depart on the morrow; and prolonged his speech until midnight(Acts 20:7).
Now concerning the collection for the saints, as I gave order to the churches of Galatia, so also do ye. Upon the first day of the week let each one of you lay by him in store, as he may prosper, that no collections be made when I come.(I Corinthians 16:1-2).