I would start with what you have and simply progress into the Erase Pro+ when you finish off the first one. I wouldn't go over 8 weeks total still. So if you happen to get two bottles of Erase Pro+ and the old bottle gets you through 2 weeks, only go for another 6 weeks. Or if you end up just getting one bottle, then use up the old and go through the entire bottle of the new one, which total should put you around 6 weeks. Does that make sense?