The attached .pdf shows an example of a possible configuration of how to setup your mail mappings so that emails of an update to the incidents are attached as notes. It also shows how to setup the mappings so that any mail attachments are stored against the incident as attachments.
As well as setting up the correct mail mappings, you will also need to refer to the Administrator Guide for information on how to configure certain keywords to activate the Update action.
Here is a link to the 7.6.2. Administrator Guide: LANDesk Service Desk Suite 7.6.2 Administrator Page 113 starts the section on how to set the keywords but you may also need to read from page 109 if you are not familiar with setting up Mail Mappings.