You can always go back and edit a resource or an activity that you have created in Moodle by choosing the 'update' option (once your editing is turned on). You can also move resources or activities in Moodle by choosing the up/down arrow icons beside the resource or activity (again, once your editing is turned on). If you have uploaded a document to the Moodle files section and wish to make a change, you will need to make the change locally and then re-upload the file. If you don't immediately see the changes, you may need to empty your cache/history in your web browser.