Loading a Premium Theme onto a Wordpress Blog and pointing at a domain name

I have bought three domain names (www.falconridge house.com, .co.uk and .eu) and have a blog up and running. At the moment the blog is linked to the www.falconridgehouse.com domain name. Unfortunately when I try to upload a premium theme to the Wordpress blog, it does not allow me to do so.

Apparently I need to also upload Wordpress.org instead of Wordpress.com and will then be able to upload the theme and link to my domain name properly. Suffice to say I have failed in my attempt to do so.

What I am looking for is assistance in sorting out this issue, with a view to also working with a reliable IT professional on a long-term basis as the company expands. To date, the IT guy I initially worked with has failed to deliver. So I need someone who is reliable and can actually complete the job they claim to be able to complete.