Is that Go Natural dry or wet?
With cats who are used to eating a certain diet it is not always a simple thing to plunk something down in front of them and say eat it. They are more likely to look at you and say bite it.
It's like someone who is used to eating prime rib as a staple in their diet suddenly being offered hamburger for their supper every night. It's not well received unless done properly.
What you should be trying to do is to mix a small amount of the new food in with the old food, increasing the new food, decreasing the old, bit by bit.
The web site given you at the first - www.catinfo.org
- gives you some great pointers on how to transition kitties to new food.