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If you didn't touch any of the files on the server, and only worked on them off-line, then copy all of them (those changed and not changed) over to the server and you're done. There is no need to spend any extra time for patching!
However, if you want to do it, you can copy the files from the server to another directory on your PC, and you can use something like
WinMerge to compare the "original" folder with the one you worked on, and then you can select the files that you've changed and create a patch as a zip file.