hi there..

today, we made our first tries with an update system. FTP download works good. We can include models, sprites..etc

But, what about new functions?

Is there a way to download a scriptfile, or textfile including a function, and use it in the game?
Or - update basic scripts with recoded ones?

Use DLLs for that, or update the whole exe (idea)

not really good.. i need that f.e. Plugins or addons, or to add new functions without letting the game download a whole exe again..

Not possible with compiled languages. You can compile new functions with the compiler, but you can't link them into the existing binary.
Go with dlls or a build a bridge for one of the scripting languages out there.