Dataset not getting cleared properly. How to clear the table schema as well

Question

  In a windows forms application, i am using a datset and binding it to a datagrid.
There are 30 buttons(for 30 tables) each of which when clicked will generate data from different tables in the datagrid.
  The problem is : when i am using Dataset as the private member of the form class , everytime i click a new tables button, the dataset is retaining the schema of the old table.
The result is the columns of old table selected + columns of the current table.

     Now if i make it a local variable of a private function of the form class that will populate the datagrid, it is working fine. But i need to accept changes from the datagrid. So i must make the dataset a member of the class not a local variable of a function.

   How to clear the dataset(rows + schema) ? Because i tried Dataset.clear() but it is just deleting the rows and tables but it is retaining the schema of the table.

 I am having only 1.1 Framework