Change geometry of mesh

Can we change geometry of mesh in three.js?
and if yes how can we do that.

I deleted some faces from geometry. after that I want to add button to discard the deleted face.
so I save geometry in another temp variable before deleting faces. and create function to overwrite
mesh geometry object with temp variable geometry object.
but nothing happened.

Please demonstrate with a live example what you do.

thanks. but i got solution.
I have to update geometry after that.

geometry.elementsNeedUpdate = true