From Online Manual
If you have Log Moderation turned on in the Category:Features and Options page, you will have an option in your Admin Control Panel to view the Moderation Log. This log shows the moderation action a Post has had such as it being: modified, deleted, split, merged, stickied, etc. Beside that you will also see the date the action occurred, the Member and their position on the Forum that did the action, along with their IP address.
You can delete items from this log that are more than 24 hours old. You can either choose to delete the selected items by selecting the checkboxes next to the item and clicking on the Remove button on the bottom of the page or just click the Remove All button to delete every Moderation Log item (except the ones that have been logged under 24 hours ago). You can also put in a member's name to view all the moderation actions they have performed on the Forum by typing their membername in: Quick Search (By: Member):.