How to replace with , working with wizard, for Previous and Next buttons?

Hi,
I'm revamping a webforms project that uses wizard. Currently the wizard has 4 steps, and is using <asp:Button> in the .aspx; in the code behind, it uses the following to navigate:
protected void StepNextButton_PreRender(object sender, EventArgs e)
{
            Button button = (Button)sender;
}
protected void StartNextButton_Load(object sender, EventArgs e)
        {

        }

        protected void CancelButton_Load(object sender, EventArgs e)
        {

        }
Now- my job is to replace the <asp:Button> with <asp:ImageButton> in .aspx, which I did; but how t ...