Update the Debian package

Add a remote with upstream repository if not already done:

$ git remote add upstream-remote https://git.torproject.org/torbutton.git

Verify the new upstream tag:

git tag -v <version>

Merge the new upstream tag:

git checkout upstream
git merge <version>
git tag upstream/<version>

Merge upstream branch to master branch:

git checkout master
git merge upstream/<version>

Update debian/changelog:

git-dch -v <version>-1

(Do not forget to set the appropriate release.)

Commit the changelog:

git commit debian/changelog

Build a new Debian package:

git-buildpackage

If everything is fine, tag the release and push the changes:

git-buildpackage --git-tag-only --git-sign-tags
git push && git push --tags

Add the Debian package to Tails

Sign the package:

debsign $CHANGES_FILE

Upload:

dupload --to tails $CHANGES_FILE