[iOS] Memory management, memory is not released when scene is changed

Hi everyone. I'm having a problem with memory that is not been released when i change the scene. Manily i use a Dictionary to store textures i display in a list ( a gui list ). I load this textures from the web. ( i know that dictionary is not the best way to store my textyres ) The problem i'm facing is that when i get into the list scene my ram get allocated ( obviously ) to store the images but when i load another scene the used ram is never released, and after two or three list scene loading the device goes out of memory and crashes. Does anyone have a trick to make my ram been released when scene is changed ?