When creating notes and other text on a drawing in AutoCAD, most design industries state that the drawing's text should be in all upper case lettering, or All Caps. This is easy enough using the Caps Lock button. Press it on and type away. It is easy to forget that the Caps Lock is on when switching from AutoCAD to email or a word processor. One way to help manage this is to leave the Caps Lock off and tell AutoCAD to always type in upper case letters. Select a multiline text object and double click it. This will open the Text Editor. Right click to bring up the options window and select the ALL CAPS option.
If you want to change the current case of text, select the text to change, right click and pick the Change Case option. Then select either Uppercase or Lowercase, depending on your needs. Here is a short video to help you see the steps described above.