unpmeric on "[Plugin: WooCommerce - excelling eCommerce] Adding Optional Extras to proucts"

I am looking to add the ability for customers to add upgrades to a product.

For example: Warranty 1 years (£20), 2 years (£30)

An example of what I am looking for can be seen here

I have been playing around with groups and read from FAQ but am unable to work out how to it. Will I need an extension?

http://wordpress.org/extend/plugins/woocommerce/