You can change an item’s category (Lodging, Dining, etc.) by dragging the item from the notebook list onto a category name on the left side:
(You can do the same thing in a multi-destination trip to drag an item into a different notebook section.)
You can also change an item's category by clicking into its details page, and then picking the new category from the menu in the blue box:
Tip #1: You can create your own categories by choosing New Category from the list on the left.
Tip #2: If you use Planapple's Save Button, you can set the category when you save the item to your trip. Planapple tries to guess the correct category for several popular sites, but you can always change Planapple’s guess in the save dialog.