Feeding your cats a vegetarian diet is not something I recommend - cats are obligate carnivores and have certain nutritonal needs that can not be met solely by plant proteins. Here is an article I have recently found (and so far just skimmed but it has a good explanation of why cats need animal proteins versus plant): click here
and by the same vet, this article on quality commercially produced canned cat foods(though I personally feel that Wellness canned, because of it's use of garlic, is not for me or my cats): and click here
This particular author/vet is into raw, which I am not, but if you wished to know more about that kind of diet, she has details.
Key to consider...switching from a dry only or primarily dry food diet to wet/canned as the primary format of food. The first article listed above also has information on why...in a nutshell..too many fillers and carbs...cats do not need sugars, whole or cracked corn, soy or wheat flour, etc., and the higher moisture content in a canned food is preferable.