I have installed elementary OS 5 and when i run
lscpu i see only 2 CPUcores working instead of 4.
I have notebook Asus E203N. Any ideas to solve it ??
Is this your CPU? If that's the case you only have 2 cores not 4. Otherwise update your question with your CPU model.
I doubt your laptop has it, but some computers allow to unblock the CPU to have more cores or to enable hyperthreading. Check inside the bios/firmware to see if there's such option.