First of all - sorry for my bad English!

Nearly two years ago I bought an iMac.
I bought Office 365 too.

One year later I changed from Office 365 to an another version (€ 58,-).

In February I installed the new version. Last week Outlook stopped working - I don't know why but I can't open anymore.

Word, Excel, Powerpoint are working perfectly only Outlook doesn't run.

I tried to install Office again but it failed . . . 

The Microsoft-Hotline told me that I have to uninstall Office first to install new.
Before uninstalling Office I have to secure my old Mails I have in Outlook.

No one at the Microsoft-Hotline could help me - except the advice to try this community.

I'm not very familiar with computer and I have no idea what to do. 

My questions:

• how can I secure my old Mails without being able to open Outlook?
• is it really necessary to uninstall before a new installation?
  - a friend of mine told me that you can rename of file: "com.microsoft.office.licesing.plist" and afterwards you can install new -
• if it is necessary to uninstall - how does it work?

Thank you for your help in advance . . . 

best regards

Friedhelm