windows forms width height xml config

I am trying to set the height and width for a simple winform using xml configuration. I can not get it right.

Code snippet:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" 
         sku=".NETFramework,Version=v4.5"/>
    </startup>
  <appSettings>
    <add key="DefaultAppPage" value="http://127.0.1.1/xampp
     /Login.php"/>  
  </appSettings>
</configuration>

Thank you for your help!