Generic world map

Hello!
I need to serve generic world map (coastline, countries, big cities, rivers). How can I remove some details from planet.pbf, so I will have smaller database?

There are many tools for manipulating/filtering data, for example:

It depends on what output format do you need and many other factors.

BTW - feel free to join Polish forum if you want to discuss things in Polish:

https://forum.openstreetmap.org/viewforum.php?id=23

You might be better off using http://www.naturalearthdata.com/.