this model is fully rigged.
to change the character go on and open human then delete Alpha_Joints and Alpha_Surface you will end up with the human armature dont delete it till you get your model that you want to change with. after you get your character if it's rigged here you can delete the human armature then attache the four robots to to the bone under the neck if your model is not rigged yet please rig it or use an empty then attache all of human and robots to it
(warning!)make sure to use ctrl+p to parent them on both ways
if you got any problem with the model or anything you can type in the comments