When we switched daycares for SS at about 26 months, our MIL took him in for an hour or so for a day before our first week. They played, hung out, talked with all the teachers, let him get familiar with the layout and rooms, meet some kids.
But other than that, pretty much cold turkey. He did ok, it took him a week or so to really adjust, but we tried to keep it positive. And remind him of all the new toys he could play with, new books, and new friends, and how exciting and fun it was. He's one of those kids that really would follow our lead... ya know?
I understand how sad it can be to leave one place, and nerve-wracking to see how the new place does. But the staff at daycares are pros at this, it's what they do. Each kid was new at some point.