But when I try to do so,this happens: The fingers don't scale,I think this has something to do with the bones,(forgive my ignorance,it is all morning that I search for an answer). It would be also fine if I could just scale the posed model,It has already got the pose that I need.
Without seeing your whole model, it is hard to say, but here is a solution to try... Here is my 'hand' rig:
Now add a new bone and parent all of the bones to it.
Now select the parent bone and scale it. All of the children bones and their meshes will scale with the parent.
It is possible you have a break in your child/parent relationship in your model? But in general all children bones scale with their parent and, if you do not have a parent bone, you can add one for this purpose.