Replacing symbols in an animation is a relatively simple action.
First of all open the file index.fla from template/flash.
You can replace a symbol in an animation using the swap function. Go to the layer in which is placed the keyframe containing the instance of that symbol and click on that specific keyframe. Let's say we want to change the "name" symbol with the "slogan" symbol. Go to the "name" layer and click on the last keyframe of the animation (as shown below). If the layer is locked unlock it clicking on the padlock icon close to the layer's name to make it editable.
Selecting a keyframe you automatically select the entire content of that keyframe. Here we have an instance of the "name" movie clip symbol. We want to change it with the "slogan" symbol.
Now that the "name" symbol is highlighted click on it to select it. The Properties palette should look like in the image above. You have a short description of that symbol: type, instance of, size, position and color. To change the selected symbol with another click on the Swap button.
The Swap symbol window pop up and from there select the symbol you want to replace the old one
Now you have on the canvas the new symbol:
As you can see now this is just another instance of the "slogan" symbol (1) but different in style, position and rotation from the other one (2)
To completely change a symbol from an animation that contains 2 or more keyframes with another one you have to swap the symbol in every keyframe of the animation