Changing the name of an iPhone in general, and specifically on version 5s, is not difficult for users. In your case, it might be because you are new to using the device and not familiar with the process. From Settings, go to General, select About, and then choose Name.
Here, you can proactively change your name, which will be displayed on your phone and when connected to a computer through iTunes...
https://Mytour.vn/change-iphone-5s-name-3612n.aspx
If you're unsure how to mute the keyboard sound for this device, you can also refer to how to mute the keyboard sound on iPhone 5. Good luck with successfully changing the name of your iPhone 5s!
