I did not understand what you meant by trashing!
But anyways, you can get a complete new kit and ditch the old kit. But you can use the new with the old. Unless they are of the exact same specs. Which is hard to find.
But you still did not mention why you need 8GB. 4GB is enough to provide you all the happiness in the world. 8GB is only for heavy apps. Gaming is fine with 4GB.