This is from BWSAYP
By making the morning nap progressively later, you can eventually make it disappear! The suggested time table below assumes that your child is at least 1yr old and normally naps at 9.30am The times might vary, depending on your child, but the principles of gradual transition remain the same.
Days 1-3: Put him down 15-30Min's later for morning nap - 9.45-10
Days 4-6: If possible, put him down 30Min's later at 10.15-10.30, give a snack at around 9-9.30. He'll sleep for 2-2.5hrs and have lunch at around 1.
Days 7 to however long it takes: Every 3 days make the nap later and later. He might have a morning snack at around 10-1.30, go down at 11.30, and wake for his lunch at around 2. You might have a few rough afternoons.
The Goal: Eventually he'll be able to stay up till noon, have lunch, play a bit and then take 1 deliciously long afternoon nap. He might have some days when he just cant make it without a short morning nap. Go with the flow but never let him sleep longer than 1hr.
My concern with this was that I couldn't tell what was happening to the afternoon nap while all this was going on as she doesn't say. But I assume that you would keep offering an afternoon nap but cutting it short to maintain bedtime until you run out of hours in the day, hopefully by this point the morning nap would be late enough to not need the catnap later anyway, at this point you may also have to do a few early nights to prevent them getting OT.
Lily was pushing her am nap on her own before she started to drop it and we had run out of hours in the day to fit both naps in with her long A times. This is where I went wrong if I had pushed the am nap forward and cut the pm nap in length I think she would of got through this easier than she did.
Thats just my opinion and hindsight is a wonderful thing