Each net has its own spacing value. Once a polygon is assigned to a net it inherits the properties of that net. The spacing property determines how much clearance there will be between objects of different nets in a filled polygon. The spacing property also determines when a DRC spacing violation will be reported between objects of different nets.
There are two ways to change the properties of nets. The first is to place your mouse over a trace or rats nest line. You can use either the keyboard shortcut p or right click on the trace or rats nest line and select properties. On the nets tab you can set the spacing value then select OK.
The 2nd option for locating nets requires that you have the Edit Panel open. If you do not have the edit panel open select View Toolbars Edit Panel. Go to the bottom of the Edit Panel and select the Project tab. Expand the PCB Node PCB Object Hierarchy PcbBoard Project Name goes here Children. Under children you will find a list of all of the objects found in your layout. Nets are labeled PcbNet Net name goes here. You can either browse the list or right click on the list and select Find to search by net name. Once you find the net right click and select properties. Select the nets tab to set the spacing then select ok.