L.D.
Start making an elimination schedule of when he is going poo and pee so that you have a good since of when he needs to go to the toilet. With my kids, after a meal is always a safe bet. Next you get rid of the diapers during the day. Explain to him that you are only going to use a pull up at night but during the day, he has to go poop and pee pee on the toilet. For the first couple of days you may want to allow him to run around with nothing on so that he gets a sense of what his body is doing and he doesn't have to deal with putting on and taking off clothes when does ended up going to the toilet by himself. As he becomes more successful you can start putting him in underwear and easy to pull down clothes. With each success, make a big deal out of it -- hoop and hollar and give him lots of tickles and such --and a sticker on his potty chart. And then if he gets "xxx" number of stickers (you decide the #), then he can earn a big prize. What ever prize it is, make sure that you either have the prize visible but out of his reach or have a picture of it so that he will keep remember what he is working for. And just remember that he is still young and kids that young tend to get so wrapped up into their play that they forget to pay attention to their bodies and do have accidents. You will need to remind him often to go to the bathroom and even force the issue sometimes even if he tells you he doesn't need to go.
I hope this helps. Being diaper-free truly is lovely.