Place your frame with the back side facing toward you on a flat work space. This positioning helps to ensure the glass does not rest against a sharp or uneven surface that may break or mar the glass panel.
Place garden gloves or work gloves over your hands.
Nestle the tip of a butter knife or a metal nail file beneath the metal tabs holding the back of frame in place.
Pry the butte knife or metal file upward so that the metal tab raises up. Repeat this action on each tab all the way around the frame. Some tabs are attached to hardware that swivels to the side. If the tabs on your frame are like this, then simply use your fingers to push the tabs to the right or left. This will loosen the back of the frame.
Remove the cardboard backing, the photo and the glass panel from the frame, placing each piece in a distinct spot on your work space.
Clean the glass panel with glass cleaner and a cloth. Allow the panel to dry before re-assembling the picture frame.