Look through
http://bikepedia.com/ for you bike to see if you can narrow down the year / model etc. Then go to giant's web-site to see if there any specific manual(s)
http://www.giant-bicycles.com/en-US/ There may be several required manuals due to the 3rd party drive train and other components. If so, then look for those manuals on those respective sites. e.g. SRAM, Shimano etc.