How can I safely remove an RSA 4096 ransom-ware virus?

My dad's computer got infected with an RSA 4096 ransom-ware virus. For those who don't know it is a virus that encrypts all the files on your PC using an RSA 4096 encryption key. Then you need to use a TOR browser to go to find a bitcoin address to pay for the key to unlock your files.

I've found a few google searches, but I don't know who to trust. Any guidance would be much appreciated.

I've included images of the screen shot my dad took of the problem.

Ransom-ware note