Although this video is a step by step instruction video of how to create a Registration Memory on the PSR SX-900 keyboard, what he is saying applies equally to all the other Yamaha keyboards. On other keyboards you would press buttons rather than the touch screen .. and other things (like setting up a footswitch to switch through the Registration Memories) operate in the same way, but you would find them in a different place.
It runs for nearly an hour, but is definitely worth watching.
PSR-SX900 Tutorial, Using Registration Memory, Download