Need help with datagrid and dataset in ASP.NET

I got it down how to fill a datagrid with a dataset. The difficulty is when I try to rewrite back to the database with the SQLDataAdapter. The page refreshes on the 'Update' button click so the DataSet is empty. How to I slurp the data off of the Datagrid back into the DataSet?

Here's some of my pseudo-code:

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The fill grid part works:

Private Sub btnFillGrid_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFillGrid.Click

Dim sqlcomm As New SqlCommand("SELECT * from WebUsers")
sqlcomm.Connection = cn

Dim sqlda As New SqlDataAdapter
sqlda.SelectCommand = sqlcomm

cn.Open()
sqlda.Fill(ds)
cn.Close()

dgUsers.DataSource = ds
dgUsers.DataBind()

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Private Sub btnGridUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGridUpdate.Click

' The Update command is declared elsewhere and it works
' the ds is declared as a dataset class variable

' need code to fill modified dataset with changes so this update will work

Dim sqlda As New SqlDataAdapter
Dim sqlupd As SQLCommand = SQLUpdateCommand1

sqlda.UpdateCommand = sqlupd

sqlupd.Connection = cn

cn.Open()
sqlda.Update(ds)
cn.Close()

End Sub