It is from the User Control Panel (UCP), not the ACP. The direct link, if you are logged in, is ucp.php?i=ucp_prefs&mode=post
Normal people… believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet. – Scott Adams
If you're looking to edit the default preferences for a specific user, it's USERS AND GROUPS tab, click Manage users, type in a username and from the Select from dropdown, select Preferences. You can not set preferences for all users as far as I know.
David Remember: You only know what you know and - you don't know what you don't know! My CDB Contributions | How to install an extension I will not be accepting translations for any of my extensions in Github - please post any translations in the appropriate topic. No support requests via PM or email as they will be ignored