Source Bone/Animation rigging help

I am in the process of porting the BF4 models into insurgency and came across a problem. I don’t know how to rig or animate anything let alone move bones around without creating more problems. So would someone please respond who is willing to fix the rigging for me so I can continue with my progress? Thanks, it would be very much aprechiated!

Heres the smd file of the character and the helmet so if anyone fixes it they can just upload it and paste the link here. Thanks!

Heres some previews of what I have so far. Notice how the hands and arms and some other things like the butt are out of place.

Well I worked all night on this trying to fix it, and I have no clue how to properly replace a player model.
The best progress I made was doing a simple head replacement on the default player model for the game.
Here is a picture of that and below I will explain the method I used to replace the model.

As you can see it totally loses its correct weights or whatever.

1st) So I launch blender and import the default player model smd, then I import the FBX of the custom model.
2nd) I rename the object and object data to the default player model one.
3rd) I drag the imported FBX into the main project and select the option to import it with automatic weights. (I tried all other options to no avail)

4th) I then delete the default player model and then export as smd.
Finally I compile the smd with crowbar and move the model into the correct folder and launch the game.

I am sure someone can help me figure out how to do this properly and easily without having to completely redo the character rigging each modification I make to the player model.

Please and thank you times a million if you help me with this.

Update: I managed to get the head on the default model with the correct rigging, but when I join the new head and the body together in blender for the export, it does something with the UV on the body and makes it all brown but the head looks fine. Anyone know how I can connect two objects together in blender and retain the old uv’s?

Edit: I fixed the uv issue by giving each object’s UV the same name via blender.