Change a CMOS battery on an Acer Aspire 6920g

As the title I think my girlfriends laptops CMOS battery's died as the clock keeps resetting to 2008 when it's been powered off, but was wondering how hard it'd likely be to dismantle and replace if anyone has any experience with changing a laptop CMOS.

It should just be accessible under the big panel on the base near the bottom right. Its a plug in type battery on a lead.

Thats better than I expected to hear - cheers!