Install WP in folder, then change to root?

Hi

I want to change from Joomla to WP, but I dont want my site to be down while I make the new WP page since it can take weeks. Is it possible that I upload the WordPress folder/installation to domain.com/folder/, and then make it be available on the domain afterwards when I am done? If yes, how can I do this the most easy way?

Thank you.