To make a NAND erase, you need to connect to your device while in uboot using minicom or cu. The device will usually be called /dev/ttyACM0. You might need to
sudo chown uucp.uucp /dev/ttyACM0
to get the necessary right (even as root). Using cu, you can then access the Neo:
cu -l /dev/ttyACM0
After connecting, you should get a prompt where you can tell u-boot to clean certain parts of the NAND memory. Before you hit enter on one of the following commands, make sure that you are *not* issuing a plain "nand erase" command - always make sure you tell it which partition to erase. If you forget this you'll brick the Neo and you'll need a debug board to recover it.
nand erase clean rootfs nand erase clean kernel
To exit cu you need to type: