To update GalCiv2 Gold--
1) Get Stardock Central
(our download manager, used to get patches or even the entire game should you not have your discs handy to install from).
2) Install it and log in with the same account you made for the forum.
3) Go to the Tools menu in SDC, and choose Register Products.
4) Pick Games on the left in the Register Products window, then find GalCiv2 in the Product pull-down menu. Enter your email address (same as forum account, again) and serial number, then click Register. If you have GC2 Gold, repeat for Dark Avatar (use the same serial).
5) Back at the main screen of SDC, pick Games on the left. You should see GalCiv2 under a Purchased Products heading on the right side. Select it and click the Update button that appears.
6) Click the + next to GalCiv2 and update Dark Avatar as well if you have it.
That should do the trick. If you encounter an error message while trying to register the serial in (4), please contact firstname.lastname@example.org.