Refilling a datagrid

I've created a drop-down list with only 3 choices and wish to fill a single datagrid depending on which of the 3 is chosen. I have 3 different datasets defined and wrote a simple "if" statement to load the datagrid. Unfortunately, i'm having trouble clearing the grid out to be able to refill it with a second, third, etc, choice.

I'm sure there is something simple I'm missing. If you think it will help, I will post my code from work tommorrow. Thanks for any help.

Ooogaleee