Thank you so much everyone! You're so kind!
Actually I was thinking to improve my RAM just because on my PC I have 4GB and when I run all the apps I need it becomes so slow (yes, I do use ccleaner, I don't have any toolbars, no virus etc...). For example when I open an outlook email with lots of images and I have more than 6 o 7 tabs of firefox open, outlook crushes or just starts not to respond (it is frustrating when happens!).
Or, if I have open more than 4 firefox tabs, it is impossible to use google voice or website full of flash animations as firefox crushes or stop working.
So, to avoid this, I was thinking to upgrade the RAM.
Why do you think ssd is so important? I'll be happy with 128 GB since I'll save everything (photo, music, etc...) on my onedrive account and open it when I need something from the browser (that hopefully doesn't crush as happens now!)
What OS are using? What Processor are you using?
How is it I can have 10 chrome tabs open, Solidworks 2015, outlook and mastercam x8 on a surface pro 3 and it not slow until my assemblies get fairly large or my mastercam files get over 10mb