Manage Users in phpBB 3
After making the setting of the Groups go to the left menu, select the link on the Manage Users then type the name of the user in the search box, and submit it.
After the completion of all this there will appear an entire overview of the link of the administration panel. In this, you can alter the password of user and email. You have also the option to delete any undesired user and his\her post.
After the setting of all if, you wish to make any changes then click on the Submit button. There are many further options are available which are facilitated for changing the user signature, group, permissions etc.