If you type a portion of your document in the wrong case, you won't have to retype it. You can change the font case from the Format menu.
This convenience will save you plenty of time should you make a mistake. However, there's an even faster way to change the font case.
Simply highlight the text you would like to change. Then press the Shift + F3 shortcut key. It will change between sentence case, all caps, and all lowercase letters. Keep pressing the shortcut key until the font is in the desired case.