I have done as per your suggestion .
But it Gives error as follows "Object reference not set to an instance of an object."

Changed code is as
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
'Dim conn As New SqlConnection(connstr1)
'Dim sql As String
'sql = "Select * from address1"
'Dim da As SqlDataAdapter
'Dim cmd As New SqlCommand(sql, conn)
'conn.Open()
'Dim ds As New DataSet()
'da = New SqlDataAdapter(sql, conn)
'da.Fill(ds, "Address1")
'maxrows = ds.Tables("Address1").Rows.Count
'inc = -1
'conn.Close()
'If next_record <= maxrows - 1 Then

If inc <> maxrows - 1 Then
inc = inc + 1
'NavigateRecords()
TextBox1.Text = ds.Tables("address1").Rows(inc).Item("rollno").ToString
TextBox2.Text = ds.Tables("address1").Rows(inc).Item("name").ToString
'inc = inc + 1
End If

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'conn.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = C:\AddressBook.mdb"
connstr1 = "server=kishorjagtap;uid=sa;pwd=kishor;database=addressbook"
Dim conn As New SqlConnection(connstr1)
Dim sql As String
sql = "Select * from address1"
Dim cmd As New SqlCommand(sql, conn)
conn.Open()
Dim ds As New DataSet()
da = New SqlDataAdapter(sql, conn)
da.Fill(ds, "Address1")
maxrows = ds.Tables("Address1").Rows.Count
inc = -1
conn.Close()
End Sub