Well, first I'd see if your 1 year old likes the taste of whole milk, give your LO some milk and see what happens. If your LO likes it, you're good to go! If not, you can try mixing milk and formula, slowly increasing the amount of milk and decreasing the amount of formula until it's all milk. Good luck!
try milk in the bottle first, by 15 months my doctor told me to have my daughter off the bottle. so he told me to take one bottle a day a way with the bottle right before bed last. so i tooke the lunch bottle first and gave her a sippy cup. then breakfast, dinner and thne lastly bedtime. it was a peace of cake, because by the time bed came she was used to the sippy cup and actually asked for it . i had to hide the bottles though. she liked to regress alittle when she found them in the drawer.
My doc said to switch straight to milk at one year. That's what we did and she didn't mind. No weaning. I also know some people who did half milk half formula for a while and gradually increased the amount of milk. Try just milk, if that doesn't work, try mixing it.