C++ :: How To Override A Method From Library That Not Contains Virtual Keywords

A quick clarification on virtual methods after reading Jumping int C++ by Alex Allain. If a user wanted to extend a class from someone elses library and override its methods that do not contain virtual methods; how would one call the overridden class if it is referred to by its super type

in other words how would someone override a method from someone elses library that does not have virtual keywords.

ie
something.h

Code:

#include <iostream>
namespace game{
class character{
public:
std::string getName(){return "character";}
};
}

main.cpp

Code:

#include <iostream>
#include <vector>
#include "something.h"
using std::vector
class protagonist : game::character{
public:
virtual std::string getName(){return "protagonist";} };

[Code]...