I was wondering, is it possible to re-size a photoshop document (.PSD) in the midst of working on it, without creating a new document and starting all over from scratch again? I've looked through all of the menus and I couldn't seem to find anything related to this. Any assistance would be appreciated! Thanks in advanced :).

It is possible - just select new imag size (Alt+Ctrl+I).
Remember that the contents will be resampled, which may give blurred result.

You can also change canvas size and re-arrange the elements without resizing.

to resize a document go edit > canvas size and change it there

to resize a document go edit > canvas size and change it there

No, you need to go edit > Image size. If you do edit > Canvas size it will either chop your image or put extra space around it. Edit > Image Size will resize the actual image and cavas.