software is avaliable for download @ blackberry.com under the software section. remember you want 4.1 one. i have an unlocked 7100g and i am on tmobile, but i downloaded the one for cingular b/c the 7100g is cingular; made sense to me.....heard it doesnt matter though as long as its 7100 os.
basically you download the .exe file and install into your computer. then you open bb desktop manager and use the application loader. it should detect that there is an upgrade. and option list comes up. then you upgrade. takes a while and it takes a while for the bb to load so be prepared to watch that hour glass.