A general rule of thumb is to use transition when swapping one content with another. You can use the RadTransitionControl for this purpose - it will animate the transition between the old and the new content.
In order to change a specific property of an element with animation, you should use the RadAnimation framework. In this case - you can use the RadFadeAnimation to animate the Opacity property of the element and when the animation is done to set the Visibility of your element to Collapsed.
The other option will be if you use the RadResizeAnimation to animate the Width/Height properties of your element.
Hope this makes it more clear. Please let us know if you need more help.
All the best,
the Telerik team
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