Yes, simply head to 'Manage Jobs' in the main menu, then click on the job which has the ad you wish to amend.
In the job menu click 'Adverts (you'll need to have the role of 'Marketing Manager' in order to see this), as shown below.

Then locate the ad you wish to amend and click 'Actions', then click  'Edit Configuration' if you wish to amend the location, duration, or budget. Or click 'Edit Advert Creative' if you wish to amend the image or text.

This is the Configuration view. Simply make you changes then click the Save Configuration button at the bottom.

This is the Edit Creative view. Simply make your changes and then click the 'Publish' button at the bottom.