Each GoPro's SD card has a limited amount of memory that you'll have to manage. You can clear the memory in a few different ways:
1) You can format the SD card from the Android's Pulse Labs app settings menu
2) You can use the Android's GoPro app to select the GoPro, View Media, then delete files individually from there
3) (The option we recommend) - on the GoPro itself, swipe down from the touch screen to access the Preferences menu, scroll down to Reset, then Format SD Card.