The jumpers are small black rectangular clips on the pcb itself. You can remove the top which leaves two small wires poking up. Removing the jumper breaks the connection at that point in the circuit. There are six jumpers in total:
J1 - this selects whether the word clock in is terminated or not. If you are syncing the unit to an external source and it is the last device in the word clock chain then J1 should be left fitted. If it is in the middle of a word clock chain then J1 should be removed for high impedance.
J2 - this selects whether the S/PDIF output is professional or consumer format. Virtually all pro and home-studio equipment will use professional S/PDIF. Some cheaper CD burners and soundcards use consumer format. J2 should be left fitted for professional format and removed for consumer format.
J3, J4, J5 and J6 - the MH444 A/D card can be used in the Focusrite Penta, TrakMaster, VoiceMaster Pro, TwinTrak Pro and TrakMaster Pro. These jumpers alter the signal level going to the converter and for use with all units apart from the Penta should be removed.
If you cannot find where the jumpers are on the card then check the picture below. J2 is marked in blue and J3, J4, J5 and J6 are circled in red. J1 is located behind the word clock connector.