Hi,
Simple, just stop WeeWX, delete your database file (it will be either /home/weewx/archive/weewx.sdb or /var/lib/weewx/weewx.sdb depending on how you installed WeeWX), connect your VP2 and reconfigure WeeWX to use the vantage driver and finally restart WeeWX. WeeWX will automatically create a new database for you.
Of course if you have customised things or are using MySQL the overall process (stop, delete, reconfigure, restart) is similar but slightly different.
Gary