Drain the old gas (tank and foat bowls).
Replace with fresh gas and a healthy dose of carb cleaner (techron gets good reviews).
Run it for about 50 miles or so.
If it ran fine before you put it away, and just has a small stumble now, carb cleaner and fresh gas should workfine.
Otherwise, gummed carbs need disassembly, and a overnight soak in carb cleaner. But, if its running, but just little rough, try the easy method first...
Gummed carbs run like total crap, and sometimes the bike won't even start-so I doubt they're that bad...