You are asking about two different things:
A) Resizing an image is an image manipulation, and has nothing to do with the part where you manipulate the image data itself. You can use the built-in methods like described here:
http://tech.pro/tutorial/620/csharp-tutorial-image-editing-saving-cropping-and-resizing[
^], or more sophisticated and fine-grained methods like
OpenCV[
^] (more precisely
EmguCV[
^])
B) How you store the image data is an other thing. You have to decide yourself by following your application requirements. I can hardly imagine a situation where you really need a different table to store the edited image - still, that scenario might exists.