Use registered username for posts

[Carlovan]

Hi all.
I'm using PhocaGuestbook version 3.0.4 with Joomla! 3.5.1 .
Unregistered users can't post anything.
I'd like to do a simple thing: when someone post something his registered username is used by default and he can't change his name.
If I hide the Name field in the form no username is used - just a null string.
Am I missing something? Can you please help me?
Thanks.

[Jan]

Hi, try to see:
https://www.phoca.cz/documents/3-phoca-g ... blic-users
Jan