Very sorry to hear about your colleague.

Upgrading from 1.12 to 4.1 is going to be a lot of work.

You need to update from 1.12 to 2.3, then from 2.3 to 3.3 and finally from 3.3 to 4.1

Also have a look at http://learn.elgg.org/en/stable/admin/upgrading.html

For each step in between you may also have to update all the 3rd party plugins you have to the working version Elgg at that step. Also you may need to run upgrades for those plugins.