Uploading a new sketch will overwrite the old one.
Are you sure it's uploading? What's the new sketch? The pin 13 LED will blink when the Arduino is rebooted no matter what, so maybe that's what you're seeing.
Uploading a new sketch will overwrite the old one.
Are you sure it's uploading? What's the new sketch? The pin 13 LED will blink when the Arduino is rebooted no matter what, so maybe that's what you're seeing.