You can remove the DDR3 memory sticks by pushing apart the silver levers on both sides and it should pop up, same as most laptops.

To access the CPU, you want to carefully peel off the aluminum tape that's stuck onto the end of the heatsink, and then removing the screw securing the heatsink as well.

Remove the 4 screws holding down the heatsink to the motherboard, and lift the heatsink.

If you're refurbishing this computer and you find the thermal paste to look very dry, it's a good idea to replace the thermal paste to significantly improve CPU temperatures, which improves the performance of the computer.