When we change how high or low the guitar sounds, we are said to be changing the pitch. We can change the pitch to accommodate a singer simply by putting a capo on the guitar to make the pitch higher. This is the simplest way of getting the guitar to match a singer’s voice.
We can also change the way the guitar sounds by changing the key. This is necesar if you have difficulty with the chords of a song you are learning. You can change the key of the song to one that uses chords you are familiar with.
Here is a video that will help you to understand how to change the key of a song . . .