You don't say exactly what he's doing (is he getting out of bed; is he waking up crying; is he having trouble falling asleep), so it's hard to give really specific suggestions. But maybe some of this info will help.
Some kids need more sleep than others. It could actually be that instead of getting the sleep he needs at night, he's getting it during the day with naps.
Between 1 year and 18 months, most kids ditch 2 naps and go to just 1. If he's taking 2 naps, cut it back to 1 per day, and don't let him sleep for hours.
I have found that it also helps a lot to keep our little guy very active during the day, and right after dinner, we go outside for another 30 minutes to an hour of outside (physical play). Then we come in and read some books, take a bath and get him ready for bed.
Our little one needs a lot of sleep, so he'll sleep from 9 pm till 7 am and then nap in the afternoon from 1 pm to 3 pm (sometimes longer, depending). Not all kids need this much sleep; some need more, some need less. (He takes after me, LOL).
Try keeping a short diary, including foods/meals, activities (the activitty info doesn't have specific), and his sleep times for a couple of weeks. You may see a pattern emerge or some clarification on what is happening.