The easiest way is to use FileBox. Go to boot/multiboot directory and delete vmlinuz-2.6.28.NIT.06 kernel. Then go to etc/multiboot.d and delete item file for same kernel (2.6.28.NIT.06). Finally go to lib/modules and delete folder 2.6.28.NIT.06.
apt-cache search nitdroid-kernel
apt-get remove nitdroid-kernel-2.6.28-06