To configure CKEditor for SharePoint on a site collection, go to the Site Actions menu in the root site of the site collection, and select the Site Settings option.
Site Settings option in the Site Actions menu for Site Collections
From the Site Collection Administration section choose the CKEditor – Site Collection Settings option.
CKEditor - Site Collection Settings option in the Site Settings page of SharePoint 2010
The CKEditor Site Collection Settings page that will open lets you configure the look and feel of CKEditor for your site collection.
CKEditor Site Collection Settings in SharePoint 2010
To change CKEditor settings, enter them into the Configuration section and click the OK button. Should you need to learn about CKEditor settings and configuration syntax, refer to the CKEditor Setting Explained section of the Administrator's Guide.