Hi Sandy,
You can customize the buttons that appear in the rich text editor toolbar using the RichTextToolsFile.xml located under C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\QuestSoftware. For example, you can simply hide or remove Undo and Redo buttons by commenting out or deleting the lines <tool name="Undo"/> and <tool name="Redo" />, save your changes, and refresh the web page, and the Undo and Redo buttons will no longer appear in the toolbar. Hope this answers your question.
Yuan