Hi K.,
My little boy (now 2) loved his 2 naps as well and I wanted to change to one nap for the same reason, so that he would be on the same lunchtime nap schedule as his friends.
We did the transition at about 15 months or so. He took an hour 10am nap and then had a second hour at about 2 or 3. That just broke our day into too many pieces for me, so what I did was gradually moved his morning nap back by half an hour at a time so that it eventually became his lunchtime nap. I made sure mornings were quiet, so that he wasn't exhausting himself too early. I'd put him to bed as late as possible without him getting hysterical and then I would let him sleep for as long as he wanted. I'd give him lunch as usual and then I kept him really busy in the afternoon so that he would be having too much fun to have his sleep. If he was really tired I would take him out in his stroller and let him have half an hour or so just to top him up, but he rarely needed that. I found that the later his morning nap became, the longer it became and the less he needed the afternoon nap.
He now goes to sleep at about 1 (but can make it to 2) and has a 3 hour nap most days. He is a little odd because he doesn't go to bed until 9pm (so that he can have some time with his Daddy in the evening) so I think some of that long afternoon sleep is to make up for the late bedtime, but even as much as he needs his sleep, I was surprised that the transition from 1 to 2 naps was fairly painless. I would just do it gradually - make the nap 1/2 an hour later for a week or so, then move it back another 1/2 an hour for another week or so and so on until it is the time you want it to be.
I hope it goes smoothly. If all else fails, just be happy you have a child who naps. I have friends who have children who rarely if ever nap and I am so grateful for my little napper.
All the best, D.