As long as I'm gonna do it, I'll use a pointer and stick with hex.
char myString[] = "Hello Again";
char *ch;
void setup() {
Serial.begin(9600);
ch = myString;
while (*ch) // exits on terminating NULL
{
if (( *ch &0xDF >= 'A' ) && ( *ch & 0xDF <= 'Z' )) *ch &= 0xDF; // so that bit 5 only gets cleared for alphas
}
Serial.println( myString );
}