The simple answer is to update your will any time there is a change in your beneficiaries, representatives, estate assets, or the tax law. The following article lists some specific dates to look for—if your will predates the listed dates you may want to come in for a technical update even if your situation has not changed.
-Dan
http://www.marketwatch.com/story/check-the-freshness-date-on-your-will-2015-06-16