Flip the frame to the reverse side and remove the frame backing to access the mat. Use a screwdriver pry to away any brads holding the backing place or unlock locking mechanisms if your frame uses these instead.
Pull the current mat and picture from the frame.
Remove tape attaching the picture to the mat. Be very careful when removing the tape to avoid tearing the picture.
Flip the picture over and center it over the new mat. The picture should rest against the reverse side of the mat. The side to be displayed should be face down.
Center the picture in the mat opening. When you are satisfied with the placement of the picture in the mat, attach it to the mat.
Use a piece of linen or surgical tape to attach each side of the picture to the new mat, creating a hinge. Apply tape vertically. A 1-inch piece of tape should cover 1/2 inch of the mat and 1/2 inch of the picture.
Clean dust or dirt from the glass front of the frame using a soft cloth.
Place the picture and new mat face down in the frame. Place your hand firmly on the back of the mat and carefully flip it over to ensure that the positioning is correct and there is no visible dust or dirt.
Replace the backing. Lock the locking mechanisms or push down the brads with a screw driver to ensure that the backing is firmly in place. Hang the picture.