2 purchase related questions, 1 design question

Running lates WP with theme version 3,2 on fleksjobbernetvaerket.dk 1) is it possible to change to another PRO theme, with purchase a new, if you aleady purchased one, or do you start all over? 2) We purchased this 'upgrade' opportunity for a year. Is it possible to take a break for this, and come back lets sat 1½ later and start paying again? 3) I'm not satisfied with the way the website acts or look. I wanna change a lot of it. However, I dont want to let people see I'm changing the site before I've done it. Can I somehow make "the new site" and when done, then put it live?