I went to a DS220+ on DSM 7, and so far it has been a deep struggle to get Owncloud to run again. First, there is sadly no community package for this combo.
Step 1: Log into your NAS as administrator and go to Main Menu → Package Center → Settings and set Trust Level to Synology Inc. and trusted publishers.
ownCloud provides ready-to-deploy packages for popular Linux distributions such as Debian, Ubuntu, Fedora, RedHat Enterprise Linux, CentOS and openSUSE. Docs & Guides · Older Versions · Release Notes · Changelog