No blogger initiated advertising, paid content or sponsored content of any kind is allowed on free hosted WordPress.com blogs.
There is only one advertising program called WordAds at WordPress.com and it’s for blogs on their own domains. Aside from a blog being accepted into WordAds http://www.wordads.co/ no blogger initiated advertising, retailing or reselling the work or products created or services provided by anyone other than yourself is allowed on free hosted wordpress.com blogs. E-commerce transactions via shopping carts and the like cannot be conducted on free blogs from and being free hosted by WordPress.com.
On free hosted WordPress.com blog we can use a contact form and/or a PayPal button for sale of only products or services created or provided by ourselves.
There is no upgrade you can purchase from WordPress.com that changes any of that. If you do require an ecommerce site, advertising, affiliate links, paid or sponsored content you can hire a web host and get a free software install from http://wordpress.org
Refer to > http://support.wordpress.com/com-vs-org/
No content is lost. You hire a web host http://wordpress.org/hosting/ and set up a WordPress.org install. Then you export your content out of the WordPress.com site and import it into the WordPress.org site.