It is challenging to change the diet of an Amazon who has been on seeds for many years, but it is possible and important. Good for you for taking this on!
My parrot lived on seeds for 20+ years, but we did successfully convert him to pellets. That was a long time ago, and you should search the archives here and google for tips on making the transition. Since he has just undergone a big change moving in with you, I wouldn't try to cut him off the seeds immediately; instead, I would try a slower transition. But you should ask people who have recently done that for advice.
As far as getting him to eat more veggies and fruits, three things: First, I agree with ImmunoGoblin to try different shapes, varieties, and cooking methods. My parrot, for example, would eat some things, like kale, raw, but other things had to be cooked. And some things that you would think a parrot would like (e.g., mango and papaya) he just wouldn't touch.
Second, parrots are very social creatures, and my parrot would try things if I ate them with him. So whenever I ate at home, I'd always have some parrot appropriate food that I would give him at the same time. Or if I was just feeding him, I would have a bit of the food at the same time. Of course, you shouldn't feed him junk, so if you are subsisting on potato chips and KFC, this won't work, but if you have a reasonably heathy diet, sharing some of your healthy food will encourage him to try new things. But there are some foods that are not good to share with parrots: chocolate, avocados, alcohol, mushrooms should never be given. Fried food, dairy, meat, food with lots of yeast (e.g., bread) and salty food should also be avoided. Also, you shouldn't bite off a piece of food to give to your parrot--apparently some bacteria in our saliva are bad for parrots. Finally, you shouldn't leave fresh food in his cup for more than a couple of hours; after that it may grow mold that could be dangerous to your bird.
Third, and somewhat controversially, I sometimes added a bit of olive oil to my parrot's fresh vegetables. I probably wouldn't do that until Jasper is off a seed-based diet. Too much fat is very bad for them. But a little bit of olive oil, on occasion, did make the veggies more attractive to my parrot, and may, in very small amounts!, be good for birds.
Finally, when giving fresh fruits and veggies, I would recommend organic, if possible. At the very least, try to either buy organic, or just don't buy, fruits and vegetables with a high pesticide load. Here is one list:
The Dirty Dozen - Foods You Should Always Buy Organic
Good luck!