In version 1.5.5:

You can customize file:
templates\{your-template}\widgets\map_popup.php

In older version <=1.5.4:

You need to change (only example for template page_homepage.php, for other template files you should open other template file):
templates\{your-template}\page_homepage.php, line 34.

Variable name depends on ID of this option/field, you can find it in your administration->Estates->Options
Pseudo variable: {option_#}, # is ID
For more details about variable, check out: http://real-estate.iwinter.com.hr/documentation/#!/property_template , section “Real estates for map on top:”

And for ajax results:
application\controllers\frontend.php, line around 2689:
$estate_obj_gen->data= …

Here you can use for example something like this:
(!empty($estate[‘option_36′])?$this->data[‘options_prefix_36′].” “.$estate[‘option_36′].” “.$this->data[‘options_suffix_36′]:”)

In your template file if you want to change autoload map popups then you should customize this part (red color), you should use CTRL+F to find this code:

values:[
            {all_estates}
                {latLng:[{gps}], adr:"{address}",  options:{ icon: "{icon}" , labelContent: ( abbrNum({option_36}) ), labelAnchor: new google.maps.Point(22, -5), labelClass: "labels", labelStyle: {opacity: 0.75} }, data:"<a style=\"color:#25863E\" href=\"{url}\">{option_2} in {address} for {option_4}</a><br />{option_3}{options_suffix_3}  {has_option_19}{option_19} bathrooms{/has_option_19}  {has_option_20}{option_20} bedrooms{/has_option_20}  {has_option_1000}Zone {option_1000}{/has_option_1000} "},
            {/all_estates}
            ],