Knowledgebase
How to disable admin notifications in Magento
If you want to disable the various notifications that show up in your Magento admin panel, you need to disable the Mage_AdminNotification module.
You can do this from the Magento admin panel > System > Configuration > Advanced section > Advanced. There click Disable Modules Output and from the drop-down menu next to Mage_AdminNotification select Disable. Click Save Config to save the change and you will no longer receive notifications such as messages about new Magento versions available.