Right, I have purchased a new theme but when I install/ edit it on Wordpress it messes with my current theme which obviously I don't want changing until I'm ready to release the new look.

So I have set up another Wordpress on my host to use so I can set this new theme up and edit it until I'm ready for it to go live.

Question I have is - once I'm ready to release it how easy, if possible is it to transform this edited theme onto my live Wordpress/website?