1/ How Can Remove the Member tab? 
2/ How to username instead full name? 
Hi @nalin_duminda,
1/ How Can Remove the Member tab?
Please navigate to Forums > Usergroups, edit the usergroup you want, and uncheck "Can View Members" and "Can View Profiles" CANs/permissions:
Related topics below: https://wpforo.com/community/how-to-and-troubleshooting-2/hide-members-tab/#post-852
https://wpforo.com/community/how-to-and-troubleshooting-2/is-it-possible-to-hide-the-member-page/#post-45943
2/ How to username instead full name?
Please note the name you show in the screenshot is the Display Name, and it can be changed in the Forum > My Profile > Account font-end page.
To get more info about wpforo Nickname, Username and Display Names please read the following FAQ topic: https://wpforo.com/community/faq/nickname-vs-username-vs-display-names/
Hi Thanks for the reply.
1/ I have already done this yet I still get the member tab 
You can check it in other usergroups to see that it workes and correctly hide the Member tab. To hide the Member tab for the admin usergroup please use the following CSS code:
#wpforo #wpforo-menu #wpf-menu .wpforo-members{
display: none;
}
The CSS code should be added in the Dashboard > Forums > Settings > Styles admin page "Custom CSS Code" textarea
2/ What I basically want is to show only show the username nothing else. is there simpler way to do this?
Please try the following CSS code:
#wpforo #wpforo-wrap .wpfl-4 .wpf-parent-post .wpf-right .wpf-content-head-top .wpf-author-name a{
display: none;
}
This worked, but unfortunately only in this place. there are several other places user's name priniting as the real name and we want it to be the Username instead the real name.
Do you have way may be function or small code snippet I can use to achieve this this requirement.
#wpforo #wpforo-wrap .wpfl-1 .wpforo-post .wpf-left .author-name a, #wpforo #wpforo-wrap .wpfl-2 .wpforo-post .wpf-left .author-name a, #wpforo #wpforo-wrap .wpfl-3 .wpforo-post .wpf-right .wpforo-post-author-data .author-name a{
display: none;
}
Hi,
Your solution just hide the name, in a instances like this
it will hide the whole name instead replace it with the user name.
Can you give a permanent solution?
Sorry for the late response.
it will hide the whole name instead replace it with the user name.
As far as I understand you want to replace the Display name with the Nicename. If yes, then I'm really sorry but there is no way to do this.