sketch uploading

Im having trouble uploading programs on my arduino leonardo board, im using a mac which keeps giving me an error saying "my device is already in use" which i fail to understand where its being used.

I used another laptop with windows saying that i havent installed my drivers properly, so what are the drivers which im failing to install..i also followed the guidelines on the website regarding selecting the port which unfortunately is not highlighted disabling my ability to access the selection port option..what can i do?..need help.