Welcome to LQ!!
First, stop thinking about drives and partitions in the Windows way. Using "fdisk -l" in a terminal, you find that Linux is on /dev/sdaX and Windows is on /dev/sdaY. (X and Y being partition numbers)
To delete Windows, all you have to do is delete that partition.
For more specific help, post the output of "sudo fdisk -l" (Run this command in a terminal, which you will find somewhere in your menus)