Select the volume,
Select everything below selected volume,
Give these elements a component name,
Select all volumes (or required volumes),
Select everything below selected volumes,
Unselect the compnent name in step 3
/Replot
OR
Select only the volumes you want
Select everything below selected volumes.
Depends on your code as to which will be easiest.
Then read the help files most importantly xSEL anmd asssociated commands.