If the box around text is indeed a "frame" in Word-speak, right-clicking in that text will show "Format Frame" at the bottom of the right-click menu. Clicking that command opens the Frame dialog, with a "Remove Frame" button at the bottom:
Caution: If the frame has "Around" text wrapping, removing the frame will move the text to the location of the anchor.
If the frame is part of the definition of the style applied to the text, you can remove all of the frames in the document that have that style by modifying the style, clicking Format > Frame in the Modify dialog, and clicking Remove Frame as above. As soon as you close the Modify dialog, all the frames will disappear.