1. Click on start and open 'Devices and Printers'
2. Right click on the Printer and select 'Printing preferences'
3. Select 'Paper' on the tabs alone the top
4. On 'paper Selection' change 'Paper Source' to 'Tray1 (A4)' from 'Tray3 (A4)'

This will reset the default tray.  If word, excel documents, etc. continue to print to wrong tray it means they have been previously printed to the wrong tray and saved.  You need to correct when printing those  documents from within the printer options too.