Hello,
to use custom logos for User Manager web interface:
1. Log in the router, using FTP or SFTP - many FTP/SFTP client applications, including freeware, are available for download
edit: I´m using FileZilla
2. Create directory named umfiles on the router, if does not already exist. Note: directory name is case-sensitive!
3. Upload your logo file (for example, logo.jpg) to that directory.
4. In User Manager Customer web page go to Settings > Style. In "Logo" field specify link to your uploaded logo, using /umfiles/ as prefix, for example, /umfiles/logo.jpg
Saludos
Uli