Changing the alt text for social icons

Hi, This may have been covered before. I could not find the topic so I apologize in advance if I am being repetitious. Is there a way of changing the alt text for social icons? I had to adapt one of the social icon links after having a less than satisfactory result with the custom icon function. The link works fine and I modified the PNG file to show the icon that I wanted in a grey scale and color form like all the other icons. All that needs to be done now is to modify the alt text to correspond to the link that I want. When I tried the custom icon function instead of replacing the existing image when the mouse pointer went over it with the hover image it just put both images side by side on the social icons menu. When the mouse pointer goes over them they both get a bit darker. Certainly not the effect that I had in mind as I wanted my personal icon to react in a similar fashion to the other social icons. Any light that you can shed on this situation would be appreciated, Steve