Place the memory foam topper on the pillow top cover of your mattress. Center the memory foam evenly so that it covers the bed completely.
Stretch a fitted sheet over the memory foam topper and the pillow top cover and around the mattress. Putting the fitted sheet on your bed might be more difficult than usual because of the added bulk, but it is manageable. The sheet will hold the memory foam topper in place on the pillow top cover.
Conduct the above steps in reverse, if you wish, by placing the memory foam topper beneath the pillow top cover so that the pillow top cover is on top.