You will need the Full Write Resources permission to perform this action.
Go to "More > Resources" in the left hand navigation menu and then select the "Items" tab. The full list of available items appears. Click on the name of the item you want to edit. You can also click on the "View" button at the end of the row.
Afterwards, the item details page will appear. Select "Edit item" from the "Actions" drop down menu in the upper right area. A pop up will appear where you can edit the details of the item. To edit questions, you would do so from the "Questions" tab by clicking on the question to edit.
Please read this article for more information on the fields that are editable.