If you have accidently deleted something you didn't wish to delete, that is no worries.
All deleted items are placed in the Trash for 2 weeks before it is deleted from the site. The Trash can can be found at the bottom of your menu when logged in as admin and has the icon of a rubbish bin.
Once in the trash, click on the item you wish to restore and click on the restore button.
It will no longer appear in the Trash and will be back from where you deleted it.