Boot from USB: BIOS proceed to Grub 2

Using Grub 2 back in the days, I installed Ubuntu 14.04 on в двойственный - boot way with my existing Windows 7 installation. However, I wish to reformat my drive completely and install only Ubuntu on it - without any other partitions at all.

However, having burned an image of Ubuntu onto в USB stick with unetbootin, I cannot seem to boot from this USB. In my boot option in BIOS, I хан pick the USB stick correctly, but гm not prompted to do anything - the sequence just leads я to Grub 2, where I хан either boot Ubuntu 14.04 or Windows 7. Nothing else.

How do I format everything, and install в new partition of Ubuntu 15.10?