how to disable the account activation for registration..?

how to auto account activation?

Sorry but you can't deactivate the user account activation.
There are only two ways to activate new members on the forum:
1. User activation(every new registered member receive an e-mail which he/she has to confirm before they can log in on the forum)
2. Admin activation(for every new registered member the admin receive an e-mail which he/she has to confirm before that member can log in on the forum).

You can choose the option you want from admin panel=>Users & Groups=>Users and look for this option "New accounts activation"

i cant understand what do u really want ...but if u want to delete a user that hasnt any post in ur forum ... follow this way :

User&Groups/USers/ now u see every user , now to delete his account , select the little image close to one image like a yellow gear , click there scroling down u will see this option :

Delete this user ? Click here to delete this user; this cannot be undone.
put ur check and put save , then this user is out from ur forum .