Main toolbar > Select and Non-Uniform Scale (on Select and Scale flyout)
Main toolbar > Select and Squash (on Select and Scale flyout)
If you transform an object using Select and Non-Uniform Scale or Select and Squash, the results may not be what you expect, especially with objects to which you have already applied one or more modifiers. This is because the transform is performed after all existing modifiers have taken effect.
You may prefer the result of applying the transform to an XForm modifier placed lower in the stack; in most cases, immediately above the object position.
Procedure
To apply Select and Non-Uniform Scale or Select and Squash to an XForm modifier in the stack:
Select the object to be scaled.
Go to the Modify panel.
In the Modifier Stack rollout, click the Modifier Stack drop-down list at the top of the rollout.
On the list, click the stack level above which you want to apply the scaling operation. Typically, this would be the object level, at the bottom of the list.
Click the Modifiers rollout > More button, and from the Modifiers list, click XForm (you may have to scroll to the bottom of the list to find it).
Click OK to exit the Modifiers list dialog.
The XForm modifier's gizmo sub-object is now active, and any transforms you make are applied to the gizmo, and thence to the object.
Apply any transforms you want to make.
You can move this transform to any other stack level using standard cut-and-paste procedures. See Modifier Stack.