Replace
dt = ExecuteQuery("UPDATE tblUsers SET UserID = " & txtUserID.Text & ", UserName = '" & txtPassword.Text & "', Password = " &
txtPassword.Text & ", LastName = '" & txtLastName.Text & "', FirstName = '" & txtFirstName.Text & "', Position = '" &
txtPosition.Text & "', Address = " & txtAddress.Text & ", EmailAddress = " & txtEmailAddress.Text & ", SSS_ID = " &
txtSSS.Text & ", ContactNumber = " & txtPhone.Text & " ")
with
dim query as string = "UPDATE tblUsers SET UserID = " & txtUserID.Text & ", UserName = '" & txtPassword.Text & "', Password = " &
txtPassword.Text & ", LastName = '" & txtLastName.Text & "', FirstName = '" & txtFirstName.Text & "', Position = '" &
txtPosition.Text & "', Address = " & txtAddress.Text & ", EmailAddress = " & txtEmailAddress.Text & ", SSS_ID = " &
txtSSS.Text & ", ContactNumber = " & txtPhone.Text & " "
Debug.WriteLine(query)
dt = ExecuteQuery(query)
and post the output of Debug.WriteLine in this thread. Because the problem is with your query it would help to know what query the DBMS is executing. Incidentally, with some constructive code formatting you can get
dim query as string = _
"UPDATE tblUsers " &
" SET UserID = " & txtUserID.Text & "," &
" UserName = '" & txtPassword.Text & "'," &
" Password = " & txtPassword.Text & "," &
" LastName = '" & txtLastName.Text & "'," &
" …