As of Aug 11, 2012 Complete now ships with a folder of blank Data and Media files so you don't have to delete the sample data by hand. Need a copy of these blank files, just ask.
To use these files, quit FileMaker (or close the SeedCodeComplete files on your FileMaker Server) then replace the SeedCodeData and SeedCodeMedia files with the ones in the folder "Blank Data and Media Files".
Deleting the sample data from Complete is the same as deleting records in any other FileMaker solution; you'll visit each of the main sections of the calendar (like "Contacts") select Records / Show all Records from FileMaker's menu (it may be greyed out if all records are already showing) and then select "Delete All Records..." from the Records menu.
Some data, like settings and Items (on the settings screen) you'll delete by clicking the red "x" beside each row you want to delete.
And when you get to the calendar, click on FileMaker's List icon (or select "View / View as List") and to the Show All / Delete All thing on the event list view.