The controls on this options page enable you to reset Merge options to default values and to clear history lists.
Reset all options
This button resets all Merge options to their initial, default values. History lists are also cleared.
This operation cannot be undone, so you may wish to save a copy of your current options using the Save options as… 
button at the bottom of the window.
Clear history lists
This button empties the history lists for file/folder comparisons and find/replace dialogs. This operation cannot be undone.