C Replace one character in an char array by another

I have the following C Code

#include <stdio.h>
int main(void){
    char c[] = "ABC"
    printf("%s ", c);
    c[1] = 'B';
    printf("%s", c);
    return 0;
}

The output I want is ABC BBC but the output I get is ABC ABC. How can I replace the first character in an String / char array?