I dont think that you can do that. Certainly not well
this is intuit's official word on it
Quicken cannot convert QuickBooks data because QuickBooks data files contain many elements for which Quicken has no support mechanism.
You can, however, convert Quicken data files (except Investment Accounts) automatically to the same or higher version of QuickBooks. This is a one-way conversion, however; once Quicken data has been converted to QuickBooks, it cannot be restored in Quicken.
i would not suggest that they discourage moving from a more expensive program to a cheaper one for any financial reasons.
The only way i have seen that even has a shot at it is to export to exel and then convert to qif and then import to quicken. I tend to think it will take longer to do that and figure out how to get things into the right places and check for errors then to just start over.