Select one or more records which are already designated as favourites, then in the expanded actions menu on the right side of the screen, select 'Remove from favourites'.
Note: If you select a mixture of records which have already been added to your favourites as well as records which have not been added to your favourites, then in the expanded actions menu on the right side of the screen, you will see both ' Make favourite' and 'Remove from favourites' options.
Immediately 'un-favourite' record
To immediately remove a record from your favourites, click on the coloured star icon associated with the record.