Find and replace HEX values

[ngudger2021]

Hi Guys, I hope somone can help me understand Hex a little,

I need to find and replace C3 91 with D1,

The code i have only changes 1 value IE C3 with D1

        
Dim fs As New FileStream("C:\Users\nick\Desktop\test.txt", FileMode.Open, FileAccess.ReadWrite)
        Dim b As Integer = fs.ReadByte()
        While b <> -1
            If b = &HC3 Then
                fs.Seek(-1, SeekOrigin.Current)
                fs.WriteByte(&HD1)
            End If
            b = fs.ReadByte()
        End While
        fs.Close()
        fs.Dispose()

can someone help me achieve this.

Also can someone tell me what &H means ??

Cheers guys