If you have previously installed Atom from another source, backup your atom directory, then remove atom package
$ cp -R ~/.atom ~/.atom_bak
$ [sudo] apt-get remove atom
Then install the latest version using the webupd8team PPA
$ [sudo] add-apt-repository ppa:webupd8team/atom && \
> [sudo] apt-get update && \
> [sudo] apt-get install atom