Refreshing gridview with new data

Question

I have a combobox and  a gridview. whenever an item from the combobox is selected , the gridview should be populated with related records.

My question is how can we refresh the datagridview with new  data and remove the old one.

 

Right now  when i click on combobox item A , the gridview displays  item A records.

Then when i select combobox item B, the gridview displays Item A and B records.

 I only want item B records to be displayed