Lenovo ThinkCentre M55e - Manual (Page 17)

4. While holding the rear of the computer chassis down, pull upward on the
handle provided to remove the PCI riser assembly and any adapters that are
currently installed.
5. Carefully take note of the location of all cable connections on the system
board. It will be necessary to reconnect them properly when installing a new
system board.
6. Disconnect all cables connected to the system board. See “Identifying parts on
the system board” on page 4.
Important
Note the cable routing. It is important to route the cables the same way
after you install the new system board.
Chapter 2. Replacing hardware 9