Go to System>Users
Choose the user who has moved office
Choose the new office from the Office drop down menu
Save the record
NOTE: Users who work from multiple offices sometimes set up multiple instances of the same user eg 'Fred Office1', 'Fred Office2', etc (often so that they can appear in different diary groups). This is NOT recommended and is better handled by creating diary groups and including the travelling negotiator/valuer/manager in the diary group. The likelihood of mistakes being made by choosing a 'wrong' version of that user is that much greater than when using a single instance of that user