Hello Powpawell,
Upgrading RAM is the best way to increase performance.
Since, you use your laptop for CAD and the other software's, anything between 6GB - 8GB of memory would be better but if you are into hardcore CAD designing, multimedia editing and stuffs then probably 16GB or higher will be better for you. But provided all these I think your processor is kinda on the slower side and bit sluggish.
Btw, your laptop (Gateway NV78 series) support a max memory of 8GB.
Conclusion: If you are not looking for another laptop just want to get the most of this laptop then upgrading your laptop's memory is the ideal choice. You can find the memory for this laptop
here. But I think you would be better off with a newer laptop which supports a minimum of 16GB with the latest Intel Core processors, probably a mobile workstation!
Hope everything works according to plan. Cheers!