iExplorer lets you view and export your Backup data to your Mac or PC for archiving or sharing, but it's not possible to delete or edit any of that data since the Backup section is actually reading the information from an iTunes backup on your computer and is not directly accessing it on your iPhone or iPad.
If you want to manage the content of any of your text messages, notes, contacts, bookmarks, etc., you'll need to do so in the apps on your iPhone or iPad. Then, once you are finished making the changes, you can refresh the backup in iExplorer to have the changes reflect there too by right-clicking on Backup in the left panel and choose Back Up Now. Just be sure to use the Export buttons to make copies of that data outside the iExplorer window before making a new backup. The article below explains more:
How to keep a safe backup with iExplorer
Or, if you would just like to delete an entire backup on your computer so that the information doesn't appear in the Browse iTunes Backups section, please see this article:
How do I delete Backups from my computer?