This hardware combination cannot run modern mainstream software, but it can handle highly specific, low-demand tasks.
A: No. The official memory limit of the processor is 2GB. If you install 4GB, the system will only recognize and use 2GB of it, so you will see no performance benefit. Your money is better spent on an SSD.
Use browsers like Pale Moon or Midori instead of Google Chrome.
Given the hardware limitations, what is a modern, realistic use for an old Atom N455 netbook? The key is to understand that it will run modern, full-featured operating systems well and to choose a lightweight OS specifically designed for low-resource hardware.
So why do people search for "Intel Atom N455 4GB RAM"? The answer:
Install content blockers like to stop resource-draining ads and scripts from loading. Restrict browsing to one or two tabs at a time.