You could completely modify the user's Display Name(first name and last name) through AD, but you have to resynchronize the User Profile in the SharePoint Central Admin.
Follow these steps:
1.Go to SharePoint CA >> click Manage service applications >> click User Profile Service Application
2.On the Manage Profile Service page, click Start Profile Synchronization >> choose the “Start Full Synchronization” option
3.On the Manage Profile Service page, click Configure Synchronization Timer Job >> click “Run Now” button
4.On the Job Definitions page, find and click “User Profile Service Application – User Profile to SharePoint Full Synchronization” >> click “Run Now” button
You could go to the Manage User Profile page to check resync whether successfully.
@Leili Vazietan
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