newbee problems with update and set

Hi guys, super Newbee here i've been looking over my code for an update button and keep getting an error"syntax by set"

private void btnUpdate_Click(object sender, EventArgs e)
         {
             SqlCommand sComm = new SqlCommand(" update Customers " +
                 "set CompanyName ='" + tboxCompanyName.Text + "', " +
                 "set ContactName ='" + tboxContactName.Text + "', " +
                 "set ContactTitle ='" + tboxContactTitle.Text + "', " +
                 "where CustomerID='" + tboxCustomerID.Text + "'", conn);
             sComm.ExecuteNonQuery();
             

         }

Can someone see what i'm doing wrong.  I've got a delete, next, previous, first, last buttons as well , they work fine but this one is giving me a headache.  THANKS