1. Purchase a 1 month trial. You don’t need to enter any credit card info, and after the purchase is complete, you will receive a license no. for a 1 month evaluation period.
2. Make sure you have access to a CalDAV/CardDAV server.
3. Copy a backup of your calendar and your contacts address book in Outlook.
4. Setup the connection first as a one-way connection. Choose who is the master (e.g. Outlook or iPhone), which means the data on the chosen device will get synced to the server. However, be aware that the sync does not delete existing data. If you currently have an address book in Outlook and in iPhone, a one-way sync would duplicate the entries in the other device. In my case I always kept Outlook as a master, and before I did the one-way sync I deleted all data on my iPhone.
5. If you are upgrading or reinstalling: Manually stop OutlookDAV (right-click on icon, then exit). You can only do this, when the sync is not running. Uninstall or upgrade OutlookDAV. Rename or delete file data.sqlite in path D:\Users\krselsrc\AppData\Roaming\Comodo OutlookDAV. You need to do this to force OutlookDAV to re-sync all entries, not just the new ones. Unfortunately, settings will be deleted at the same time.

1. Before doing anything, I recommend to delete calendar entries in the past with large attachments. To find them, follow Delete large attachments in Calendar items. This will speed up future syncs and also free some space in Outlook.

If you are replacing the current address book with the one you synced to ownCloud from Outlook, consider to delete the address book before syncing, otherwise you might end up with duplicated contact entries. Here are the necessary steps:

1. Check first whether you created any contact entries on the phone which were not synced back to Outlook before. iContacts+ can help you with this as it allows to sort all contacts by creation date, youngest item first.
2. Go to Settings –> Mail, Contacts, Calendars and make sure that all accounts' Contacts sync is off, including the account created to sync with the ownCloud server. Disabling Contact sync from mail accounts will prompt the iPhone to ask whether you want to remove the contacts from the phone.
3. Go to Settings –> iCloud and disable Contacts sync. This will prompt the iPhone to ask whether you want to remove the contacts from the phone.
4. If Contacts sync was disabled in iCloud, enable it first and allow some time to sync the contacts to the cloud. After that, disable it again and proceed as described before.
5. Now that all contacts are removed from the phone, go back to Settings –> Mail, Contacts, Calendars and enable Contacts sync for the ownCloud server.

If you are replacing the calendar on the phone with a new calendar on the server, do not change the sync settings on the phone. Delete the address book on the server and make sure the sync settings on the computer are set to one-way (Outlook to Server).

See How to Delete All Contacts on an iPhone