you have 2 questions
1) can i upgrade ram?
Go to crucial.com and use their automatic detector. and it will tell you if you can or cannot
2)will the extra memory improve your performance?
Depends on if the tasks you are doing are being constrained by memory.
If you go to TaskManager and observe the memory usage. If the Memory usage is approaching or exceeding the 4GB then you may get a performance benefit.
There are more complex diagnostics to really check memory usage but Task Manager is good enough for a general analysis.
But if memory usage is lower than 4GB then you won't get a performance benefit
You could upgrade to 8gb, But it is dependent upon what you do, if your editing and rendering while running a bunch of programs at once, it would help. I have 8gb on my PC and honestly i never really go over 2.5gb even while gaming.
Like said above, check the ram usage in task manager and go from there.