Elephants don't have hands!
elephants do not have 1 hand... they have four legs
It's fun answering these types of questions, as they're usually semantics arguments. In other words, there's an infinite amount of valid answers. I'll demonstrate:
As the first answerer suggested, you can lift a one-handed elephant in the same way you'd lift a two-handed elephant.
As the second answerer suggested, elephants do not have hands, so you are making up an imaginary animal; how do you lift an imaginary thing?
Combining the first two answers, you can lift an imaginary one-handed elephant in the same way you'd lift an imaginary two-handed elephant: with an imaginary crane.
If you meant to phrase the question as, "With one hand, how do you lift an elephant," you'll have a whole other possibility of answers. My favorite take is the physicist vs. mathematician stances:
Mathematician: Define "lifting" as the action that takes place when an area vector from the elephant's chest is antiparallel to an area vector from the person's palm on an overhead stretch, with his wrist bent back 90 degrees. Therefore, a human performing a one-hand handstand on the elephant is lifting the elephant.
Physicist: Use a crane using only one hand.
See? Lots of plausible answers.
the same way you lift a two handed elephant :)