Now that you have bought a sofa bed mattress, the next step is to install it on your sofa bed. Sofa bed mattresses are normally attached with buckles or ties and can be detached and reattached easily. After taking out the old foam, use a duster or a vacuum cleaner to clean the internal frame of your bed. As soon as you are done cleaning the frame, put the new mattress, fasten the ties or buckles and that is that. Your job is done and you can peacefully enjoy your new sofa bed.