The how-to when you are out of hand wash, unscrew the pump from your 500mL hand wash bottle. Carefully fill to the bottle's neck using the 1L refill bottle (a funnel makes this easier). Replace the pump in the 500mL bottle and you are good to go.
But first, read this
Patch test before use. Store below 30°C. For external use only. Avoid contact with your eyes (if you get some in there, rinse immediately with water). If you experience irritation after use, please discontinue.