Moved iTunes library to external hard drive but songs on PCs hard drive

I have read and followed the instructions on this forum for backing up and moving my iTunes library to an external hard drive (G:)(Back up and restore your iTunes library on your PC - Apple Support). After backing up the library and selecting the iTunes Media folder located on the external drive, I checked the file location of some of the songs in iTunes and see they are still located on the C: drive. A quick test showed that if I uploaded a CD that was not in the library before moving it to the external drive, it was stored on the external hard drive. I want iTunes to use the the files on the external drive so I can delete the library on my hard drive. I am not sure what to do now. Hope you can help.