I would strongly advise to download and read the maintenance manual for the procedure. Also - double check the parts listing in the manual for the correct upgrade path.
One other thing to consider is that a CPU upgrade will bring more heat and draw more power to run than what was originally in the notebook. This means that your cooling solutions may not be adequate and run constantly. This may require a new heatsink and fan combo to be installed that can better cool the CPU.
I do not work for Lenovo, I only provide suggestions based on my personal willingness to help others. All advice and comments are based on my experience, and do not reflect Lenovo policy, terms or conditions.