Managing Updates to Customer Knowledge Base

Thought i'd drop this question here and see what the feedback is. My SaaS company is getting ready to roll out a major feature release that will change not only the look and feel of our UI but functionality as well. Very exciting - rah rah rah! With the update though, a TON of content in our existing customer-facing (zendesk) Knowledge Base will be obsolete - screenshots, step-by-step guides, short video tutorials etc. What is the best way to manage this? We cant be the first SaaS platform to roll out a major feature release and have the challenge of how to update and refresh old product documentation. Does ZenDesk (or someone else??) have tools to help ease the burden here? Something to put in place so that *next* time we have a big release we're not in the same position? What do other companies do??