On the Volunteer Family page there is the option to view and update the volunteer summary.
The summary is auto-populated from the bio a volunteer enters on their e-application form.
To update it, use the text box to overtype/edit the existing summary, then press the update button.
Having clicked update, you'll be back on the summary page and will be able to see the change to the Last Updated... text.
A note will also be added to record each change to the summary and highlighted in green.