No need to get all excited and go the full gamut here. For starters, Haagen, you could just swap out the rear cassette. If that does the trick then you're done. No need to spend big buckage up front upgrading the entire drivetrain for that particular bike. We are after all talking about a Giant Upland here, not an NRS.

Here in the States I recently purchased several Shimano HG-70/105 grade 9-speed rear cassettes for $17 after a coupon and on sale at Nashbar. I don't know what kind of deals you can procure in Ozzie Land but I doubt they are that inexpensive.