If you go the page that is for the year in the category of sets you're looking to change, you should see an "(Edit)" link next to each set. Inthere, provided the set is not a major release and that you have the correct permission level (which is sounds like you do), you can edit Toatl Cards (and a couple other fields) there. Please double-check all changes you plan to make to ensure your info is correct and you've selected the correct set (I only say this out of personal experiences - sigh).
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).