Hello,
Microsoft Silverlight is not a 4GB app. It is just like Adobe Flash player. It is used for a browser plugin. That is it. Unless you have a app installed for development of Silverlight.
It is Microsoft version o ftha flash player. That is it. So what ever is taking up that 4GB it isnt Silverlight. And if the fodler says that then you have problems. My Silverlight folder is only a few MB big.
Cheers,
Mak