You are able to change the target of your application to a different platform as long as it has the status "Unpaid". Once the application gets "Paid" status, you are not able to change its target, unless you duplicate it.
Therefore, in order to change the target of your app, go to its Dashboard.
By clicking the drop-down menu for the "Target" field, you have the option to select Native iPhone, iPad, Android, Kindle platform or WebApp. Select the one you want your app to be created for.