This is as easy as opening a .zip file in emacs. You will be shown a dired style file browser (in Zip-Archive mode) in which you can open files and edit and save them as normal, without having to extract them from the archive. You can also do a few other things to the files in the archive – use C-h m to see the help for the current major mode.

Similarly, opening a .tar (or even a compressed .tar.gz) archive will open the contents in Tar mode. This is very similar to the above, except that once you edit a file, you have to go back to the Tar mode buffer and save that to update the original archive file (this is automatic in Zip-Archive mode).