First and most importantly you need to know which drive (if you have more than one) you are working with.
Normally, I recommend only having one drive (the intended OS drive) connected during the process so as not to cause any unintended consequences.
Then on the first screen you see suggesting you pick a language and keyboard layout, hold the shift key and strike the F10 key.
That should produce a command prompt Window.
In the command prompt window type
diskpart
hit enter and give it a minute to evoke the diskpart prompt, then type
list disk
hit enter
then type
select disk 0 (where disk 0 zero is the disk you wish to wipe)
hit enter
then type
clean (absolutely critical that you are certain that you are on the correct disk as this will completely wipe the drive / all volume / partition information)
hit enter
then type
exit
that's all there is to it.
For UEFI / Secure Boot / GPT configurations I like to use Rufus to construct the boot media from the ISO.
You need to configure it as follows.
View attachment 2009
http://rufus.akeo.ie/