Updating checkbox From custom buttons

I have tried so many times for the checkbox to be updated to true when a file is uploaded, however, despite trying and also searching on google, I still couldn’t change the checkbox value.. Is there anything wrong with the codes?

 if({!Account.Check__c } == false)
     {
          var c = new sforce.SObject("Account");
          c.id = "{!Account.Id}";
          c.Check__c = true;
          result = sforce.connection.update([c]); }