Full size day bed serves as a couch or sofa during the day and as a bed at night. A full size day bed has rails or other decorative trim element operating as arms and a backrest. A daybed typically uses a twin-size mattress. If you want a mattress that is bigger than a twin for your daybed, you must change the frame of the bed. Remember that the only difference between a twin size mattress and a full-size is a width, since the length remains the same.
Remove the mattress from the bed and examine the structure. Remove the backrest and arms around daybed include these features. Screw the arms and back, leaving only the legs and the frame or base of the mattress. Create a frame from the four pieces of plywood. Use the two pieces top and bottom and the longer pieces on the sides. Screw wood screws through of each part; attach the wood in a large box. Move the box next to the full size day bed and line the new frame with old daybed. Cover the top of the frame with the larger plywood panel. Attach wood screws every 2 inches around the bed; secure the upper surface of the frame.