error on refresh command..

Question

can someone teach me how to create an efficient refresh command used in loading values in datagrid.
im using VB.net and MySQL for the database. my problem occurs when i try to refresh the values in the datagrid after it has been updated, the returned value is just appended on the previous value. for example i have 2 rows in the datagriedview,when i click the refresh button, the rows become 4. same value. is there other way to do this? please help me. thanx in advance.