How do I download and install a new ring tone?

I want to use a downloaded mp3 for my ring tone on my Blackberry Priv.

Find the file you want. Download it. And remember where you saved it, then go to Settings > Sound & notification > Phone ringtone. When you go there, if you have a file manager installed, it will ask if you wish to use that or 'Media Storage'. Choose the file manager you have installed and browse to where you have the file saved and choose it.