degrouping stl file objects on blender I have imported an stl file to blender and its separate objects I can`t figure  out how to deselect the objects.

I have tried all the selection and deselection option
s 
The file was made on 123D
this is the STL file I imported to blender and I want to un-group the highlighted objects any suggestion thanks?
Use the Separate function. 

Enter Edit Mode (Tab)

Highlight (select) the object you are breaking apart, press space, type "separate" (or use the keyboard shortcut P) then pick "Loose Parts" from the list of options.







To help you select the parts, you can select one vertex of or the specific item you want to separtate and press CtrlL to select all of the connected vertices. Then separate using P

A different way to select different parts is using Box select (CtrlB