All The Tropes:Bureaucrats
Bureaucrats are those with ultimate power regarding promoting and demoting others on ATT. as they are the only ones who can remove administrator flags from other admins with impunity, and are the only ones who can grant the bureaucrat right to others. In practice, we run more like an adhocracy, but 'crats are the people who make sure the wiki keeps running, and help to resolve debates.
Labster, Looney Toons, GethN7 and robkelk are the only bureaucrats entrusted to run this great wiki with honesty and integrity.
Do note this power is not used lightly, and in the event of abuse by anyone with this right, please report such abuse to Miraheze Staff (the Stewards' noticeboard is the best place to report alleged wrongdoing by the All The Tropes bureaucrats), and if they find that right is abused, they can remove the bureaucrat right from the bureaucrat in question.
See below for those with even higher power than bureaucrats.
Miraheze Staff
Stewards
The Miraheze Stewards have all access to any wikis, and they do user renames. You can contact Miraheze Stewards on Stewards' noticeboard.
Sysadmins
The Miraheze servers are run by the House of SysAdmins. Contact them about downtime, server bugs, and the like. They're easiest to contact on the #miraheze IRC channel - see here for a list of Miraheze IRC channels.
Or you may also contact Miraheze system administrators by emailing sysadmin
miraheze.org