downloads - How to replace Windows XP with Ubuntu?

I have found out that they will be phasing out windows XP which I currently use. My brother recommended I switch to Ubuntu.

Firstly, my computer itself is ancient, around 10 years old, will I be able to use Ubuntu?

My other questions include what happens if I download this and it doesn't work? What happens to XP if I do download? Yes, my questions may be simple to some, but I'm just a little unsure of how all this works.