Hello and welcome to the forum. Years ago I had a dog that came to me on this and I found it quite strange - it looked like a breakfast cereal - a bit like a cross between muesli and corn flakes. I took her off it quite quickly. Don't know if it still looks like this. Anyway, which type of Vitalin are you feeding? By coincidence I looked at these on the Dog Food Directory just a few weeks ago and the score varies, Adult and Puppy Plus being the better varieties.
I'm assuming that you need to continue with dry food. Depending on the food you choose, you could be thinking about continuing with puppy or going onto junior. Some might say just go onto adult and with my breed that is what I did last year when my pup reached about seven or eight months. I see no problem in going to an adult food as long as it has the right kibble size and is of very good quality with a high protein level. It should have a named meat source at the head of the list of ingredients. The more meat, the better the food. Then decide whether you want to be grain free. If you are not bothered about this, just make sure there is no wheat, maize and perhaps white rice in the formula. Vitamin has corn and oats in it so maybe grain free might be best seeing as how he has gone off it.
There are so many great products on the market these days and it is hard to advise you on which to choose but here are a few examples of the better ones: Canagan, Millie's Wolfheart, Orijen, Eden. There are more and if you do a search on the Dog Food Directory you can put the filters in that you require. You will then get suggestions which you can check out. Of those, I have used Canagan and I think it is a good dog food.
Personally, like TinyPlanets, I like cold pressed foods because they have not been subjected to the high temperatures that kibble is exposed to, therefore leaving more of the nutriments intact. If you would like to look at these, some of them are: Markus Muhle, Lupo, Black Angus and my favourite, Gentle. They tend to be for all life stages.
All of these foods are more expensive than Vitalin but don't be put off by that because dogs tend to need smaller meals so you will see an empty bowl but the dog's nutrition will be better. Smaller poos too.