Get a new drive, and a USB stick, and follow these instructions . Once you get to the installation part, stop your PC, take out your windows drive, put in the new one, and continue.

After the installation, stop the PC, put the windows drive back in, together with the linux drive, and start the PC back up. Select linux at boot up. You should then be able to access your Windows drive from Linux and safely copy your data to the Linux drive.

Keep using linux until you feel comfortable and only then can you wipe your Windows drive and extend linux onto it.