Cannot find any settings for this. Can it be done by skin edit?

There isnt a way in which to change this action. Search will always be by what the system deems to be the most relevant to the search criteria entered

Ok, then I suggest that the default can be selected in the ACP. At least on our forum sorting on Date is more relevant than Relevancy.
Should also be possible to sort on number of replies and views.

Please feel free to post up within the feedback area what you would like to see in that area