Can I change vertex buffer's size?

Can I change vertex buffer's size?

Maybe it's a stupid question but I actually don't know - is it possible to
change vertex buffer's size after it's been already created (with
CreateBuffer())? If so, how do I update its data (with both Map() and
UpdateSubresource()) when the new data contains more/less vertices?
I'm interested in vertex buffers and dx11 but the question probably
applies also to index buffers and opengl.