Just use the counter.
By clicking on the "Next" increases by one.
By clicking on the "back" button, reduces it to one.
Each time you press a button after changing the value of counter, you should assigning his value to the property "text" of the button
For example:
private int counter;
private void btnNext_Click(object sender, EventArgs e)
{
counter++;
if(counter < 21 && counter > 0 )
{
myLabel.Text = counter.ToStreing();
}
}
private void btnBack_Click(object sender, EventArgs e)
{
counter--;
if(counter < 21 && counter > 0 )
{
myLabel.Text = counter.ToStreing();
}
}
Of course you can use a function,for example SetLabel, and call it from both places .....
Regards,
Alex.