Board Thread:Support Requests - Designing Your Wiki/@comment-5927228-20130101032316/@comment-4018164-20130101053546

You can by going to the user's contributions page, and at the top, where it says: For USERNAME (talk | block | block log | uploads | logs | deleted user contributions | user rights management) Press the link "user rights management". You can also do that by entering his user name to Special:UserRights.

For uploading a logo, name it File:Wiki-wordmark.png.Logos should be 65 pixels height and 250 pixels wide. If it tells you to upload it via the Theme Designer, go to the admin tools page in your wiki and select the theme designer page.