I currently use AMD A6 5200 APU processor, with linux (Zorin OS 15) as operating system. I have 4 GB of ram. I can run blender 2.92 at a good speed however it does slow down when I have over 4000 particles during scenes or complex node groups but I can get around that, however what I can’t get around is animation playback in viewport. It gets really slow sometimes with around 2 armatures in scenes even with less complicated animation. All I need is around 24 fps of viewport animation playback.How much better performance can I get if I upgrade to 8 gb of ram (because this is only something I would be able to afford right now so I would like to use my money wisely)
Use a System Monitor or Task Manager tool or similar (eg, ‘top’ on Linux) to see if your system is using all of its memory when you’re doing a large, slow operation. If you still have free memory then that isn’t the bottleneck. If, however, the memory runs out and the system starts swapping to disk (known as “page faults” or “virtual memory swapping”) then you would benefit from adding more memory.
More RAM is generally-speaking better at the 4 GB level; but another thing you should seriously take into account is RAM speed. I have a local rendering machine which has an old (but surprisingly reliable) MSI 760GM-P34 motherboard; which has a cap of 16 GB. I've got all 16 GB now, but it also started out with only 8 GB. The significant improvement came when I threw out the 8 GB stick--which was 1066 MHz--and replaced it with a 1600 MHz stick. Everything is much smoother now.
This is generally true for any software which alters memory on a regular basis, Blender is certainly included whether you're using a CPU or GPU; especially when you're working with physics or particle systems and doing a lot of baking. I suggest you look at the available speeds for your motherboard, check on what you're using now, and consider shifting it up to the fastest available.
If you add more ram both the GPU and CPU will benefit (as you have an APU in your system) The APU uses system memory for graphical processing and you would notice a great improvement within games and video editing programs, therefore any large scenes in blender that is eating your ram currently would benefit.
The main bottleneck itself (if system memory is not the issue) would be the CPU itself, While AMD APU's are great for the price, there are upgrades you could make to your machine for better results, such as a new CPU, dedicated graphics card, SSD etc, but this is all costly but worth considering in the future if you continue to use blender or even decide to use it to make money.
A recommendation would be to aim for 8-16gb of memory to get the most out of of your system.
this is all based on personal experience with an old APU and gaming/photoshop, a small improvement was there after upgrading from 4gb to 16gb but decided on a total rebuild to achieve much better results.