Briefly...
The most important things to copy are your ~/.emacs.d
directory and your init file (see C-hig (emacs)Init File
for the different filenames this might have, or check with C-hv user-init-file
).
See C-hig (emacs)Windows HOME
regarding where the .emacs.d
directory should live on your Windows system.
Note the comments in that Info node on the site-lisp
directory as well, in case you've been using elisp libraries in there (possibly without realising), as they can form part of your Emacs configuration as well.
Any byte-compiled elisp (.elc
files) should remain compatible so long as you're moving to an equal-or-newer version of Emacs (which sounds likely in this case). Natuarally things do change between releases, though, and it's possible to encounter incompatibilities when upgrading, but I wouldn't worry about that in advance -- try the latest version first, and if you run into problems that you can't solve (which shouldn't be very likely), you can always install the version of Emacs you were originally using.