My workspace keeps track of all the generations created; how do I delete them?

Hi, 

As the title says, my artboard keeps all generations of my images.This slows things down considerably.The only solution I've found is to clear my browser's cache and history to get a fresh artboard.Before, the artboard would clear itself every time I left the page for a while. This no longer happens.The same thing happens with the app.I'm using an Android smartphone.Any ideas?Thanks in advance.