In order to can update your Pimcore stack you must do the followin.
- Opening a ssh connection to your deploy.
- Execute the following commands:
chmod g+x /opt/bitnami/apps/pimcore/htdocs/pimcore/lib/Pimcore/Update.php
chmod -R g+w /opt/bitnami/apps/pimcore/htdocs/vendor/*
- Go to the web interface and update as normal.
Please let us know if this solves the issue.