Hey, guys, don't give up; arm yourselves!
Educate yourselves on which ingredients are healthy, which cause the least harm, and which are totally unacceptable. Then read up on the many ways cats can be enticed, tricked, cajoled and bamboozled into eating healthier foods. Once you've got that ammunition, do some studying on the huge variety of canned products available, pick out some new foods for your cats (I recommend no less than three, in rotation, but the more, the better) and go for it.
The TruthAboutPetFood.com site has a large catalog of ingredient-related information, but there are actually quite a few resources on this topic. Your best bet, for an in-depth understanding of the manufacturing process, the tricks used in creating the "ingredients lists", ingredient sourcing and naming as well as what's truly behind the names, I recommend picking up any of the several books on the topic. In my opinion, Susan Thixton's "Buyer Beware" is the most detailed and easy to read, but any of them will give you the info you need to feel confident when you hit the pet food aisles.
CatInfo.org, RawFedCats.org, Feline-Nutrition.org and many other sites all have transition articles of one sort or another. Read as many as you can, since you never know just which trick will be exactly the one to which your cat responds.
Use petfooddirect.com to start your product reviews. They offer a huge selection, and both ingredients and analysis are available on every item.
Finally, be patient, wily and persistent; you're in charge and your kitty's well-being is dependent upon you. You have to out-wait, out-fox and out-maneuver the little rascal.
This can sometimes takes weeks or months, but it can be done.
Never give up!
AC