First, you'll need to take him to an Avian Vet in your area to rule out physical problems like infections and/or internal/external parasites.
Once bird has a clean bill of health, then turn your attention to diet. Parrots do very well on an organic, high quality pelleted diet like Harrisons. Tracie carries that here as well as a few others, so you can make an informed decision. An all seed diet, even with the addition of fruit and veggies is lacking in basic nutrition and proteins. Seeds provide a lot of fat and carbs but not much in the protein and overall balanced nutrition area.You can always sprout any leftover seeds because seed sprouts are perfect protein for birds and other small animals. Sprout your seeds inside and not in any soil. If you need further instructions, write back in, and I'll tell you how we do it. Sprouts need to be fed right away or within a 24-48 hour period and then start the process again. Always fresh, all the time.
For a bird eating seeds, it takes time to change over to pellets and here is a great article written by an Avian Vet about how to go about it: http://www.parrot-and-conure-world.com/switching-birds-to-pellets.html
It would be best to take your bird into Avian Vet for an exam before making any changes in diet because birds ill or becoming that way tend to go off their feed if offered new items, so make sure he is healthy enough to begin getting healthier.
