how to change a design in realtime
 

If you've updated a design for your paysite, should you change it ALL in like one day, or should you change it gradually, i.e. a splash page today, the new join page in 2 weeks, the new tour in another 2 weeks, etc...

why would you do it gradually? to test clicktroughs?

To get the message across that you are doing an update, but to not LOSE traffic due to people thinking its something new and strange, to familiarize users with the new design but one page at a time...

For me there is great uncertainty on sales levels for a new design, will it be more or less, who can tell?

Nope. Just add a "Newly Redesigned!" graphic on it. Gradually doing it would seem a little unprofessional. Just my :2 cents: