A family of Microsoft word processing software products for creating web, email, and print documents.
Perhaps you have applied the All Caps font property. Ctrl+Shift+A should remove it, or you can right-click, choose Font..., and clear the check box.
Another possibility is that the font in use has only uppercase, but that is unlikely in your situation.
If the text really has been typed using Caps Lock, then you can use Shift+F3to change case; if you don't get the desired case by repeatedly pressing Shift+F3 (which cycles through three choices that vary depending on the text selected), use the Change Case button in the Font group of the Home tab.