There is limited information we can give you to the specifics. If you aren't comfortable doing it, then take it to a shop.
Simply put, you need to take the bowl off the carb, spray it with cleaner and loosen up the float. Chances are good you should rebuild the carb, but just a quick clean would probably get it running again.
If you buy a service manual, it will give you more specific instructions on some do it yourself maintenance you can do, but without being there, we can't offer much more help than just generic 'do this do that' type of advise.
The do this do that advise currently, is take the bowl off and spray it with cleaner to loosen up the float.