Loosen the screw on the faceplate of the wrench. Remove both the screw and the faceplate.
Remove all of the parts. Inspect each part as you remove it to ensure that you have no broken parts.
If any part seems to be broken or rusty, you will want to replace it.
Clean each part separately by wiping with a damp cloth.
Oil each part lightly with lithium grease. You can apply the oil by spraying the grease on a dry cloth and then wiping each part.
Reassemble the wrench.