Well, my daughter just drank whole milk with no problem. I just switched and she drank it. Straight.
My son, I had to transition him, because he refused. So, I started with 2 ounces breastmilk or formula, with the rest whole milk. In a bottle. I did this until he got used to it. Then, once he got used to that, for awhile... then I gradually increased the whole milk proportions.
There is no one single way of doing it... you need to go by YOUR child's cues and transitioning.
For my son, the whole transition to 100% whole milk... took more than a couple of months.
But as I said, my daughter just drank whole milk with NO problems. And I didn't have to transition her.
Both my kids were breastfed.
I... gave my kids whole milk, on demand. In other words, I did not 'schedule' it nor only feed it to them at meals. They could drink it whenever... .and they drank as much as they drank.
Babies/kids... 'like' drinking milk from a 'bottle'.... because it has a 'nipple'on it. A 'nipple' is where milk comes from... it is instinct. Thus, they will often refuse, to drink milk, from a cup or sippy.
"Whole Milk" is important and recommended for 1-2 years old. Because, the "milk fats" in it is an important nutrient for brain development.
all the best,
Susan