Re : How to rename names in the navigation?
Your menu is done with the templates application_menu.
So there are nothing to do with the user menu in the data base.
1) the easier way - to be able to upgrade later with no problem - is to change you current application_menu template module with your own user menu module.
Go into admin -> modules. Create a new user menu at the bottom ex: "my_application_menu" insert the user menu "Application menu" , you will see on the right {menu id=42}. Save it
Go into assigned modules, assign this new user menu "my_application_menu" to the left column. Test. (if it is showing, clean the cache admin-> system admin -> delete modules/cache, templates_c)
If ok, delete the old menu
2) you can also directly change templates/modules/mod-application_menu.tpl , you will find the substring betweeen {/tr}. But after you will have to keep the update for future upgrade.