Switch to the Master Database.
Find the common template you use for your pages inside of the Template Manager. I use one just called "Page" that inherits from the General\BaseTemplate template. The BaseTemplate template has a field called Body which is a RTE field. Find that field of the BaseTemplate and then paste one of the following lines into the source field.
I used the rich text full because I want my editors to have the full RTE Toolbar and all the buttons available to them. But you could also use any of the following.
/sitecore/system/settings/html editor profiles/rich text default
/sitecore/system/settings/html editor profiles/rich text full
/sitecore/system/settings/html editor profiles/rich text ide
/sitecore/system/settings/html editor profiles/rich text medium
Let me know if you have questions, it took me awhile to figure this out, so I may be able to help you if you can't get it working.