Calculated fields allow to combine values from other fields in one new field making use of a vbscript formula (excel like formula).
When a new field is made or when the formula behind such field is updated the values shown in the calculated field will not be updated as long as no depending field value was changed.
Through the database manager it is now possible to update the field value for all members of a list at once. In the database manager navigate to the field and open the edit option. At the bottom of the edit box a dropdown list with all the available list is shown. Click the list for which the update must be done and run the update.
Note that for larger lists (> 100 items) this may take some time.