How Do Negotiate A Pay Rise

I Work as an on-site engineer for a Solutions provider company and i have recently been pondering on how to negotiate a pay-rise. I was employed by this company to provide cover on a site on Microsoft Applications. My role as, since then(8 months ago)increased to things like Network Administration, Hardware Fixing and other forms of troubleshooting. Now i recently discovered how much my company gets from the site i work at and the difference with my salary is about ?60,000.I dont really want todisclose how i got this information but i’m rather desperate and my salary is very decent either