You configure Ushahidi v2.X through four tabs (addons, settings, manage and users) on the administration dashboard, http://www.example.com/admin, where example.com is the URL of your Ushahidi deployment.

If you want to make changes to Ushahidi v2.X that aren't in these tabs, you should also check out the Ushahidi v2.X developer guide

 

There's more information in the Ushahidi manual prepared by Anahi.