As far as I understand your requirements you want the RadWindow to resize according to its content as Shinu also suggests. If so, please either set AutoSize="true" or call it thorugh code with or wiothout a parameter to turn on/off the animation. You can find a very similar online demo below:
Another option is to simply set explicit width/height through the Width
properties (thir default values are 300px) - this is the better solution if the images are with the same size because executing scripts influences teh performance and if you do not need this it is better to simply specify the size.
If this is not what you want, please provide a more detailed explanations and I will do my best to help.
the Telerik team