Hi for general deck maintenance and how replace please check out this blog:
http://www.treadmillsrepair.co.uk/2015/02/how-to-reinforce-treadmill-running-deck.html
http://www.treadmillsrepair.co.uk/2013/08/treadmill-running-deck-removal-and.html
http://www.treadmillsrepair.co.uk/2014/08/weekly-treadmill-maintenance.html

if you're keen a purchase a replacement decks some can be found here:
http://www.partsfortreadmill.com/catalogsearch/result/?q=deck

F3 deck
L,w,d
130 x 66 x 1.94 cm