You can setup raid with 2 drives of the same capacity to create 1 big drive, although its recommended you dont set a raid config on a drive that your useing as your currunt OS drive.
Use cloning software like clonezilla, macrium reflect, or some other. If they are both WD drives, WD has a lite version of acronis that can clone drives. It may even work on other drive manufacturer's drives, but I'm uncertain on this.