There is nothing changing the sabbath from saturday to sunday as far as i know. However in acts, they meet on the first day of the week (sunday) and paul tells the corinthians to set aside money for collection on the first day of the week. Some think this is when Sunday worship started, but there doesnt seem to be a clear answer. With that said, honoring the sabbath is the only of the 10 commandments not reiterated in the new testament. As Jesus says, the sabbath was made for man, (for our rest). I dont think the day of the week matters. Every day should be a day of worship, but setting aside one special day isnt a bad thing either. As long as you're worshipping in spirit and truth, I dont think the actual day matters as Paul says:
Colossians 2:16
Freedom From Human Rules
16 Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day.