My daughter transitioned out of her morning nap at 18 months. My son transitioned just before 15 months.
Dropping the morning nap was a tough transition for the kids! I went back and forth (2 naps vs. 1 nap) for a couple of weeks -- and it never seemed like I did the right choice on the right day!! I wish I had some great tips, but it just seemed to work itself out over 2-3 weeks. Hang in there!
PS...Here are some research statistics I've been given about naps:
12 months old = 17% of children are taking one afternoon nap, while 82% take two naps
15 months old = 56% are taking one afternoon nap, while 43% are taking two naps
18 months old = 77% are taking one afternoon nap, while
22% are taking two naps
21 months old = 88% are taking one afternoon nap
24 months old = 95% are taking one afternoon nap