Xobor.com - official support forum

I do not want the ability for public to register on forum, would like to remove 'registration' from menu and use the 'invite members' function

Please advise

Even if you find a way to remove the registration link, the folks you invite will still have to register to join.

Just control your users by having a sensible registration procedure ie: Admin - Users - Groups: Then under the "Activating New Members" section then select either....
"Activate new members manually in the administration menu"
or
"New members have to confirm the activation e-mail and be activated manually in the administration menu"
That way folks can register, but their accounts will not be active until you activate them, and you have full control over who can join your board.

You might want to consider giving different groups different read/write priviledges. Like stopping casual unregistered visitors from being able to read everything that's been posted. Or limiting what newly activated members can see and do until you trust them. Also you could put a "Mods Only" forum up, and limit read priviledges to only Mods.
That lot is under Admin - Forum - Home, then click on each forum to take you to the individual 'Edit forum' pages to give the different groups different access