You have to establish a cadence of updates for different assets, which will vary based on how they are used and your market dynamics. Personas don't change often, so revisting them every 6 months might be enough, but if you are on a competitive market it may require a quarterly or more frequent update of competitive battlecards.
The important thing is to establish a schedule for revisions and set time aside for updating those materials. Another part of your process should be communication to the sales team and others that might use them. Depending on how drastic the update was (e.g. minor edits vs major overhauls) you will also want to have different ways of notifiying the team. A Slack message about a minor update could be good enough but you probably want to do a full enablement session for major revisions that could impact a sales person's abilty to deliver the message or close a deal.
In sum:
1. Identify 'expiration dates' for all your assets
2. Establish a cadence for the revisions and updates
3. Block time on your calendar to work on the updates
4. Agree w/ the sales teams and others on the best way to communicate those updates