You would have a helluvatime yanking the cranks off by hand. You can possibly tap them off with hammer and piece of pipe but it will most likely deform/destroy the crank arms.

Another method would be to use a forked tie-rod separator type tool and hammer...but you will need to be careful not to damage the frame.

The 2 best ways would be to acquire the correct puller tool to thread into the crank arm or find a good shop that has one and pay the small cost to have it done (most likely $5-$10).

-j