removing of mobo. to a new casing



There is a clip that you squeeze to remove the 24 pin power.
There is usually also an additional 4 pin or 8 pin connector on the motherboard with the same clip.
 


It is hard to muck it up as long as you don't try to remove the CPU heat sink from the CPU.
Moving the motherboard with the CPU and RAM together is easy.
Don't screw anything up too tight.
Connectors generally only go in one way and shouldn't need to be forced.
Try to touch something metal before touching computer components so you don't zap them (you know that static charge you get sometimes on windy days or synthetic carpets).
Good luck.