After the artifacts are generated and signed, you can run the following script under the folder tools, to upload them into the staging directory:
$ ./upload_artifacts.sh
This script will create a remote directory named openwhisk-<version>-<pre_release_version> under the staging directory, and push all the files available locally under openwhisk-<version>-<pre_release_version> upstream. It will overwrite the old files or directories, if the directory openwhisk-<version>-<pre_release_version> is available as a svn folder.