how to get more fps?

Without upgrading hardware (And if you're running windows):
Select "High Performance" in power options
Close unnecessary apps that aren't required while gaming
Have the latest graphics drivers
Depending on the game, go in the settings and lower overall graphics options and disable vsync
Go into the games configuration and make changes there (Youtube tutorials can be found)
In task manager, set the task priority of the game to "High", if you don't know how to do this then you can find videos on how to do so on youtube.

Overclock your CPU and Graphics card if supported (Plenty of tutorials online) (Keep in mind it might decrease the lifespan)

Also, some applications claim to boost fps such as https://store.steampowered.com/app/38430...1_7_15__13 but idk if it makes a huge difference or not

Upgrading hardware:
Get more ram (8gb ram for most games should be fine but some newer games are a bit more demanding so you should consider getting 16gb instead)
Get a good graphics card and CPU (Make sure you have a motherboard that supports the CPU and Graphics card you choose and make sure you have a big enough power supply.)
Make sure you have a look at game requirements for games you like (Don't go overkill)