First of all you need to set up a subdomain. When it's done, copy all files from directory http://bellydancedreams.co.uk/bellydance-blog/ to subdomain root.

Finally you have to edit /conf/_basic_config.php file and set $baseurl = 'http://bellydance-blog.bellydanecdreams.co.uk/';

Hey Sam:

Can I do the same to transport a B2evo (3.3.3) installation on a subdirectory (www.mysite.com/beta) to the root (www.mysite.com), where i have an old b2evo install (1.10.2)?

I made the beta directory for testing purposes, even sharing the same DB. Now everything on the beta directory seems ok, and I want to transport it to the root.

Thanks

Sure, but you have to delete all old files.
And don't forget to backup the database.