How to tell if you need more RAM
Here’s how:

Press the “Ctrl” + “Alt” + “Delete” key. Now click on “Task Manager” and select the “Performance” tab. Look just under midway down on the right and you will see a box labeled “Physical Memory (K)”. Read the Total right under that. That is your installed memory (in kilobytes). If you want to convert it to MB, divide it by 1024. Now look at the box to it’s left that says “Commit Charge (K). The total there will be how much memory is being used. You will also see a “Peak” under that total which tells the highest amount of memory used since the last reboot. If the Peak is lower than the “Physical Memory” total, then you don’t need additional memory. If the total Commit Charge is higher than the Physical Memory Total, then additional memory would give you a significant performance boost because of how much of the memory your system is using with the Operating System and applications.

good explanation