Will upgrading RAM make my PC or laptop faster? PC upgrade speed boost

Will more memory make a difference?

Whether or not the extra memory will make a noticeable difference will depend on how you use your PC and whether or not you have many applications running simultaneously. Adding extra memory will certainly allow your PC to cope much better with having multiple browser tabs open at the same time. At the time of writing we're using a PC running the Google Chrome browser, which is currently using over 3GB of RAM all by itself.
When your PC runs out of available RAM, it starts using the hard drive instead. This is much, much slower than RAM and will cause your PC to slow down. It's likely that heavy use of a web browser will push overall memory requirements beyond your available 4GB, so increasing this to 8GB will prevent such slow-downs.
However, if you're very much a one-tab-at-a-time person, you may notice less of an improvement. You may find that you start to change the way you use your PC after the upgrade as it will be able to cope with much heavier use without starting to struggle.
Bear in mind that upgrading your hard disk to an SSD is likely to provide a bigger performance increase. See install an SSD into your PC for a step-by-step guide.