Edit cell on a DataGridView - vb.net

Question

How can I edit a cell on a DataGridView? When I run the project I want to edit the cell and then click a Button.
This is my code:
Public Class Form1
Dim con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=db.accdb")
'SELECT employ.id, employ.name, employ.adress, employ.phone FROM employ;
Sub New()
' This call is required by the designer.
InitializeComponent()
loadAll()
' Add any initialization after the InitializeComponent() call.
End Sub
Sub loadAll()
Dim da As New OleDbDataAdapter("SELECT employ.id, employ.name, employ.adress, employ.phone FROM employ;", con)
Dim dt As New DataTable()
da.Fill(dt)
DataGridView1.Rows.Clear()
For x = 0 To dt.Rows.Count - 1
DataGridView1.Rows.Add()
DataGridView1(0, x).Value = dt.Rows(x)(0).ToString()
DataGridView1(1, x).Value = dt.Rows(x)(1).ToString()
DataGridView1(2, x).Value = dt.Rows(x)(2).ToString()
DataGridView1(3, x).Value = dt.Rows(x)(3).ToString()
Next
End Sub
Private Sub DataGridView1_CellDoubleClick(sender As Object, e As DataGridViewCellEventArgs) Handles DataGridView1.CellDoubleClick
DataGridView1.ReadOnly = False
DataGridView1.EditMode = DataGridViewEditMode.EditOnEnter
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
DataGridView1.ReadOnly = True
DataGridView1.SelectionMode = DataGridViewSelectionMode.FullRowSelect
Dim i As Integer
For i = 0 To DataGridView1.RowCount - 1
Dim name As String = DataGridView1(1, i).Value.ToString()
Next
Dim Str As String = String.Format("update employ set name='{0}' where id= i", Name, DataGridView1(0, DataGridView1.SelectedRows(0).Index).Value.ToString())
Dim cmd As New OleDbCommand(Str, con)
con.Open()
cmd.ExecuteNonQuery()
con.Close()
End Sub
End Class
How can this be done please?