How to gain weight and muscle in a healthy way?

<body>I'm eighteen about 6'1'' and only about 140 pounds. However; I am very physically fit and toned. Thus my question is how can i gain weight, to turn into muscle, in a healthy manor if i already eat six medium sized meals a day? <img src='http://4092e72-sgr0g7wb0g0d71oefh.hop.clickbank.net/' width='1' height='1' /> </body>