Clean Up Memory After Closing Window In Wpf?

I've created an app, which puts windows onto the desktop. When i click on the window it creates a new window and passes the first window's Items collection to the second window's Items collection. Opening the second window adds around 2-4 megs of memory to the app's mem usage. Now if i close the second window, the memory still stays on the same level as when the window was opened. When closing the window, i reset the Items property and clear all images that i'm using in it. It has a wrappanel with some elements, that's also cleared using the .clear function of the wrappanel.children. What else should i do to free up the memory?