Hey Rudy, you can actually change the field of view (FOV) within the GoPro settings. You can choose from Wide, Medium and Narrow FOV's. If you press continuously onto the on/off button until you see the wrench then press on the top capture button you will enter settings. The first selection press the capture button again. This will take you into the video settings. Press on/off twice and hit the capture button which will then allow you to choose between the 3 FOV's.
If you scratched the lens that is on the protective shell then GoPro sales a screen replacement for $20. The link to it is below.
Now if you scratched the conical lens on the main GoPro camera, I do not believe there is a user accessible replacement for it. You would have to contact GoPro and probably have to send it in for a replacement.