I have two main Outlook identities and want to combine them to save memory

I am using Microsoft Outlook for Mac 2011 (v 14.5.7). I have discovered I have two main identities.  One identity has data records and a database. The data records include mailing list, rules, signatures, etc. The other identity has data records, a database and, separately, a mailing list, rules and signatures. My problem is that there seems a lot of duplication which is using a lot of memory. My question, how can I identify the files that I am using and are most current, and delete the others?  I am running OSX 10.10.3 on a Mac Air. I don't know how it happened; I'm the only person using this computer.

Thanks, John