Renaming username on mediawiki

Log in your cPanel on your server then enter on phpMyAdmin and execute these SQL commands:

UPDATE LOW_PRIORITY user SET user_name=’NewUsername’ WHERE user_name=’OldUsername’;
UPDATE LOW_PRIORITY user_newtalk SET user_ip=’NewUsername’ WHERE user_ip=’OldUsername’;
UPDATE LOW_PRIORITY cur SET cur_user_text=’NewUsername’ WHERE cur_user_text=’OldUsername’;
UPDATE LOW_PRIORITY old SET old_user_text=’NewUsername’ WHERE old_user_text=’OldUsername’;
UPDATE LOW_PRIORITY archive SET ar_user_text=’NewUsername’ WHERE ar_user_text=’OldUsername’;
UPDATE LOW_PRIORITY ipblocks SET ipb_address=’NewUsername’ WHERE ipb_address=’OldUsername’;
UPDATE LOW_PRIORITY image SET img_user_text=’NewUsername’ WHERE img_user_text=’OldUsername’;
UPDATE LOW_PRIORITY oldimage SET oi_user_text=’NewUsername’ WHERE oi_user_text=’OldUsername’;
UPDATE LOW_PRIORITY recentchanges SET rc_user_text=’NewUsername’ WHERE rc_user_text=’OldUsername’;

Just replace the tables names with your prefix wiki used, for example case you used “boo” as prefix then the above table will be named foouser, fooarchive, fooipblocks and so on.