If the text page you wish to edit is linked in the table of contents, you can click on the title and it will take you to the page.
If it is not linked, you can go to Manage → Content and either search for the text page’s title in the Title box or filter the type by Text Page and hit filter. The text page should appear below. Click on the title to open it.
Click the Edit button in the menu bar under the title to make changes to the content.
To change the formatting of your content, use the buttons in the Main Text box toolbar. While your site’s toolbar may have slightly different buttons, or the buttons may be in a different order, the function of the buttons from left to right is typically: