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