[ubuntu] Oh dear .... 16.04 UEFI dilemma

Good evening/day to one and all.

I'm not new to Ubuntu at all, but have just acquired a used Asus K55V. What I am totally new to is UEFI.

Can I not just disable UEFI, wipe the whole HD and install a lovely fresh version of 16.04?

If not I have to go to bed, but would so like to finish my clean 100% Ubuntu single boot install.

Thank you guys ..... very much for the advice.

PS I am booted from a 16.04 USB drive without any issue whatever. In 'Setup' the usb drive is called "UEFI: Generic Flash Disk 8.07"