updating from 2.9 to 3.4

I have just inherited our association website which is in desperate need of updating. It is still on version 2.9.1. I would like to get this updated but know that there is a good chance I will lose all of my plugins, etc. if I do so. What is the easiest way to get this backed up and/or updated?

There is already an issue with 1 plugin (DM Album) that stopped functioning some time within the last year. I’m hoping to tackle that issue after the update. Can anyone confirm that the old WordPress version may be what’s causing DM Album to not work properly?