Chaning PayPal Billing Frequency Code

I recently created a PayPal subscription button to put on my landing page and I created four different payment plans for my customers that they can select via a dropdown menu



I am having difficulty setting the proper billing frequency for each payment option. For example, I want the annual to be billed every 12 months, bi-annual every 6 months, etc.

I've been searching Google for help and have only found articles saying that it needs to be changed through your PayPal HTML button link. After playing around with this I haven't had much luck. Does anyone know how to fix this problem?

Thank you...

My code is below:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="WPMYBVN4VHP7E">
<table>
<tr><td><input type="hidden" name="on0" value="Payment Options">Payment Options</td></tr><tr><td><select name="os0">
<option value="Annual Plan: 1 Year = 50 cents a day">Annual Plan: 1 Year = 50 cents a day : $182.50 USD - monthly</option>
<option value="Semi-annual Plan: 6 Months = 75 cents a day">Semi-annual Plan: 6 Months = 75 cents a day : $135.00 USD - monthly</option>
<option value="Quarterly Plan: 3 Months= $1.00 a day">Quarterly Plan: 3 Months= $1.00 a day : $90.00 USD - monthly</option>
<option value="Monthly Plan: $1.50 a day">Monthly Plan: $1.50 a day : $45.00 USD - monthly</option>
</select> </td></tr>
</table>
<input type="hidden" name="currency_code" value="USD">
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_subscribeCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>