They're in .obj format, right? You can put them anywhere. Load your character from the Library, select the head, and then choose Load Morph Target from the Object menu. Poser will ask for the location of the morph. Point it toward whereever you placed the head morph, give it a likely-sounding label, and click OK. The new morph will appear in the parameter dials, at the top of the list. Remember that morph targets are designed for specific figures, and won't work on others. If you have a Posette morph, it won't work on Victoria. Likewise, morphs are designed to work on specific body parts, so you can't apply a head morph to the chest. To keep the morph, you'll have to resave the character to the Figure Library, using the Plus button at the bottom of the Library Palette.