I'll break down a couple things you can do get your computer working the way it was originally. If you using your laptop for normal stuff and not gaming. You got a good setup. You don't need more RAM you just need to perform a few maintenance task.
Firstly, if you haven't cleaned your registry in a while. This is necessary. Your registry holds all the information regarding updates, installs, un-installs etc. Each one of those events has a key. and that key need your PC's resources. So, if you should clean this up. Do a registry scan if you got more than 20 errors you should clean it.
2. Clear your Windows cache files, this your temporary file. It can grow up to a large volume and stop your computer from using RAM properly. In a sense slow it down by preventing it from using free space.
3. Manage your startups. Your excess CPU usage is due to too many programs running in the background. You can cut these to barebones by alter your msconfig.
Other great tip is increasing your virtual memory to simulate more RAM. This will give you a bit more resources for multiple program use or CPU heavy programs. Check the link to alter your virtual memory spec.
Hope this link helps. Shows you how to do everything step by step. You should get a least 30% more resources and speed if you follow the tips.
http://www.delete-computer-history.com/how-to-speed-up-my-computer.html