Changing navigation menu size

I am trying to change the height of my navigation menu. I found on firebug that what I need to do is change the line-height:inherit to line-height:0 to make this happen. This is what it looks like on firebug. Can someone tell me now how I do this?

‘border:0;
font-family:inherit;
font-size:inherit;
font-style:inherit;
font-variant:inherit;
font-weight:inherit;
line-height:0;
margin:0;
padding:0;
vertical-align:baseline;
}’