Dell OptiPlex 330 User Manual page 206

6 Disconnect all cables from the system board. Note the routing of all cables
as you remove them so that you can reroute them correctly after installing
the new system board.
7 Remove the remaining seven screws from the system board. (Four other
screws were removed with the heat sink assembly.)
8 Slide the system board assembly toward the front of the computer, and
then lift the board up and away.
System Board Screws
1 system board
9 Place the system board that you just removed next to the replacement
system board to compare and ensure they are identical.
206
Mini Tower Computer Parts
1
2 screws (7)
2