Thinkpads are really nice about actually labelling which screws you need to remove what.
I believe if the symbol for motherboard. Removing any screws with this symbol near the hole should let you access the motherboard. In some cases you may need to remove the keyboard
That's these screws.
Depending on why you need access to the motherboard, you might just need to remove the ram screws, and in some cases ram is under the palmrest.
All of this information along with disassembly instructions can be found in the Hardware Maintenance Manual for this particular model.