rename postal code to zip code

in search/location/ > Advanced search there does not appear to be a way to add the [Postal code] field to the search. I only have
-Country
-State/Province
-City
-map
-Locate Address
-Lat
-Long
-Distance

Also if you search by clicking on the map (great feature!) and then saying Distance 20 miles > search. If you then wish to widen it to 30 miles you have to re click on the map each time or manually alter the keywords eg
rom:52.57634993749885,-0.263671875,20,mi