Both the menus are different so you have to change the string of the main (upper) menu and sub menu separately.

There are two records for two menu items. Just find the correct one and change it. If you want to do modifications, better way is create separate module (addone) inheriting excising one for keep maintainability. Just create a new module and inherit old one and create a view with same menu records with same ids. change as you wants. It will replace excising one

<menuitem 
    name="Human Resources"          
    id="hr.menu_hr_root"          
    groups="base.group_hr_manager,base.group_hr_user,base.group_user,your_module.new_permission_1,your_module.new_permission_2,"          
    sequence="90"/>