If you are stuck with an N455 machine and want it to run as fast as possible, don't just focus on the RAM. Follow these steps:

Avoid heavy builds of Chrome. Try Pale Moon or Midori , which are designed for lower-spec hardware.

Using lightweight Linux distros that make 2GB feel like 4GB.

Even if you manage to find a rare board that accepts a 4GB module, the N455's single-core architecture becomes the primary bottleneck long before you hit the memory ceiling.