Only if you know for certain that you are running out of memory in specific circumstances. Open Windows resource monitor and click on the memory tab. Open all your normal stuff like you would always do and see if you run low on memory. If you don't, then adding memory probably isn't going to help much. I honestly think though that having 8GB of memory should really be a bare minimum these days.
At 4GB, depending on which operating system version and which bit version of it you are running, 32 or 64 bit, it's probably a bit low for todays machines. If you have a 32bit version of Windows, 4GB is all you can use anyhow.